P8 - WHOLE TOPIC GCSE FORCES

Summary

This educational video explores fundamental physics concepts, focusing on forces. It distinguishes between scalar and vector quantities, explaining their properties with examples like temperature and weight. The video delves into force types, categorizing them as contact and non-contact, and illustrates this with examples like friction and gravity. It introduces Newton's laws, particularly the third law, demonstrating action and reaction forces. It also covers resultant forces, free body diagrams, and the importance of the center of mass for stability. The video concludes with an introduction to moments, levers, and gears, explaining how they function and their applications in everyday life.

Takeaways

• 🔢 Scalar quantities have only magnitude, like temperature, mass, distance, and speed.
• 🧭 Vector quantities have both magnitude and direction, such as weight, displacement, acceleration, and velocity.
• 🌐 Weight is a vector quantity because it always pulls downward due to gravity.
• 🏠 Displacement is the straight-line distance between two points in a specific direction, as opposed to distance which can be longer due to a winding path.
• 🤲 Forces can be contact forces, like friction, or non-contact forces, like gravity and magnetic forces.
• 🧲 Non-contact forces include magnetic attraction/repulsion, gravity, and electrostatic forces within atoms.
• 🛠 Newton's third law of motion states that for every action, there is an equal and opposite reaction.
• 📚 Free body diagrams are used to visualize all the forces acting on an object, such as weight and normal force.
• 🚗 Forces can cause objects to accelerate or decelerate; the resultant force is the net force acting on an object.
• 🔄 Resultant forces can act in different directions, like a plane taking off, which has both upward and forward forces.
• 🎛 The center of mass is important for stability, especially in vehicles, and is the point through which the weight of an object can be considered to act.

Q & A

What is the difference between scalar and vector quantities?

Scalar quantities have only size, such as temperature, mass, distance, and speed. Vector quantities have both size and direction, like weight, displacement, acceleration, and velocity.

Why is weight considered a vector quantity?

Weight is a vector quantity because it has both magnitude (size) and direction, which is always downward towards the center of the Earth.

Can you provide an example of a non-contact force?

Examples of non-contact forces include magnetic forces (attraction and repulsion), gravity (acting on us all the time), and electrostatic forces (attractive forces between positive and negative charges in an atom).

What is the difference between contact and non-contact forces?

Contact forces occur when two objects are touching, like friction. Non-contact forces act over a distance without touching, such as gravity and magnetic forces.

How does air resistance act as a contact force?

Air resistance is a contact force because it is the interaction between moving objects and the air particles, which slows down the object due to friction.

What is Newton's third law of motion?

Newton's third law of motion states that for every action, there is an equal and opposite reaction. When one object exerts a force on another, it experiences an equal and opposite force in return.

What is a free body diagram and why is it used?

A free body diagram is a drawing that shows all the forces acting on an object. It is used to analyze the net force on an object, which can help determine if the object is in equilibrium or if it will accelerate.

How can you determine if a car is accelerating or decelerating using forces?

If the driving force of a car is greater than the frictional force, the car will accelerate. If the frictional force is greater than the driving force, the car will decelerate.

What is the significance of the center of mass in an object?

The center of mass is the point where the weight of an object is considered to be concentrated. It's important for stability, especially in transportation, to prevent objects like vehicles from tipping over.

How does the size of a gear affect its speed and force?

A smaller gear will rotate faster but with less force, while a larger gear will rotate slower but with more force. This principle is used in bicycles to change gears for different riding conditions.

What is a moment and how is it calculated?

A moment is a turning force around a fixed point. It is calculated by multiplying the force applied by the distance from the pivot (force x distance), and the result is in newton meters.

Outlines

00:00

🔬 Introduction to Forces

The paragraph introduces the concept of forces within the context of physics, distinguishing between scalar and vector quantities. Scalars such as temperature and mass have only magnitude, while vectors like displacement and velocity have both magnitude and direction. Forces, a type of vector quantity, are pushes or pulls exerted by one object on another and are categorized into contact and non-contact forces. Contact forces include friction and air resistance, while non-contact forces encompass gravity and electrostatic forces. The paragraph also introduces Newton's third law of motion, which states that forces between objects are equal and opposite.

05:01

📚 Forces in Action

This section delves into the practical application of forces, using a tractor pulling a car out of mud as an example. It explains the concept of free body diagrams to analyze forces acting on an object, such as the weight of a book and the normal force from a table. Newton's first law is referenced to describe the state of rest and the necessity of an external force to initiate movement. The paragraph further discusses the balance of forces using a car as an example, illustrating how driving force and friction affect the car's motion. It introduces the concept of resultant force and how it can be calculated using vector addition, with examples including an accelerating car and a plane taking off.

10:04

🚢 Resultant Forces and Center of Mass

The paragraph explores the calculation of resultant forces, particularly when forces are applied at angles, using a ship being pulled by two smaller ships as an example. It explains how to determine the magnitude of the resultant force using scaled diagrams and trigonometry. The concept of the center of mass is introduced, emphasizing its importance for stability, especially in the transport industry. The center of mass is described as the point through which the mass of an object can be considered to act, and its location is crucial for the stability of objects, especially vehicles.

15:06

🔧 Moments, Levers, and Gears

This section discusses moments, which are the turning forces around a fixed point, using examples like a door opening or a spanner turning a screw. It explains how moments are calculated by multiplying the force applied by the distance from the pivot. The paragraph then covers levers, such as crowbars and spanners, which are used to increase force or change the distance over which it is applied. It also touches on the equilibrium of moments, using a seesaw as an example to demonstrate how to calculate the weight or distance of an object based on the moments of other objects. Finally, the paragraph introduces gears and how they alter the speed and force between a driving mechanism and a driven part, explaining the relationship between gear size and the effort required to turn them.

20:08

🚴‍♂️ Gears and Cycling

The final paragraph focuses on the practical application of gears in bicycles. It explains how changing gears affects the cycling effort and speed, with smaller gears at the back and larger ones at the front making cycling harder due to the increased force required. The concept of gear ratios is introduced, explaining how a one-to-one ratio makes cycling easier, which is beneficial when climbing steep hills. The paragraph concludes with a call to action for viewers to like and subscribe to the channel for more educational content.

Keywords

💡Scalar Quantities

Scalar quantities are physical quantities that only have magnitude and no direction. They are fundamental to understanding the basic concepts in physics. In the video, scalar quantities are introduced as quantities that 'just have size', such as temperature, mass, distance, and speed. These are used to describe properties that do not involve direction, which is a key distinction from vector quantities.

💡Vector Quantities

Vector quantities are physical quantities that have both magnitude and direction. They are crucial for understanding motion and forces in physics. The video explains that vector quantities 'have size and direction', and examples given include weight, displacement, acceleration, and velocity. These are essential for describing how objects move and interact through space.

💡Displacement

Displacement is a vector quantity that represents the change in position of an object. It is defined as the straight-line distance and direction from an object's initial position to its final position. In the video, displacement is contrasted with distance by illustrating a scenario of walking from a house to a school. The video uses a drawing to show that displacement is the direct line between the two points, whereas distance includes all the twists and turns of the path walked.

💡Force

Force is a vector quantity that represents an interaction causing a change in the motion of an object. The video defines force as 'a specific type of vector quantity' that occurs 'when one object puts a push or a pull on another object'. Forces can be contact forces, like friction, or non-contact forces, like gravity or magnetic forces. Understanding force is central to the study of physics, as it governs the motion of objects.

💡Contact Forces

Contact forces are forces that occur when two objects are touching. The video mentions air resistance and friction as examples of contact forces. Air resistance is described as a force that occurs when air particles slow down an object, and friction is the force that occurs when two surfaces slide or tend to slide against each other, such as when rubbing hands together.

💡Non-Contact Forces

Non-contact forces are forces that act over a distance without direct contact between objects. The video gives examples of non-contact forces such as gravity, which pulls objects towards each other without touching, and electrostatic forces, which occur between charged particles within atoms. These forces are important for understanding phenomena that occur without physical contact.

💡Newton's Third Law of Motion

Newton's Third Law of Motion states that for every action, there is an equal and opposite reaction. This law is crucial for understanding the interactions between objects. The video uses the example of a boxer punching a bag to illustrate this concept, explaining that the force exerted by the boxer on the bag is met with an equal and opposite force from the bag on the boxer's hand.

💡Free Body Diagrams

Free body diagrams are graphical representations that show all the forces acting on an object. They are used to analyze the motion of objects by considering all the forces involved. In the video, free body diagrams are used to illustrate the forces acting on a book resting on a table, such as the weight of the book and the normal force exerted by the table.

💡Resultant Force

The resultant force is the single force that represents the vector sum of all the forces acting on an object. It is crucial for determining the net effect of multiple forces. The video explains how to calculate the resultant force using diagrams, such as when a car is accelerating or decelerating, where the driving force and friction are compared to find the net force causing the acceleration or deceleration.

💡Center of Mass

The center of mass is the point at which the weighted relative position of an object's mass is balanced. It is important for understanding the stability and balance of objects. The video explains that for symmetrical objects, the center of mass is at the point of symmetry, but for asymmetrical objects, it is found using a plumb line and a clamp stand. The concept is applied to explain why certain vehicles might tip over if their center of mass is too high or too far to one side.

💡Moment

A moment is a measure of a force's tendency to cause a body to rotate about a specific point or axis. It is calculated as the product of the force and the perpendicular distance from the force to the pivot point. The video uses examples like opening a door or using a spanner to illustrate moments, explaining how the size of the moment depends on the force applied and the distance from the pivot.

Highlights

Introduction to scalar and vector quantities in physics.

Examples of scalar quantities: temperature, mass, distance, and speed.

Examples of vector quantities: weight, displacement, acceleration, and velocity.

Explanation of the difference between displacement and distance using a house and school example.

Forces as a specific type of vector quantity involving push or pull on an object.

Classification of forces into contact and non-contact forces.

Examples of non-contact forces: magnetism, gravity, and electrostatic forces.

Examples of contact forces: air resistance and friction.

Newton's third law of motion: action and reaction forces.

Use of free body diagrams to analyze forces acting on an object.

Explanation of balanced forces using the example of a book resting on a table.

Illustration of unbalanced forces with an example of a car's driving force and friction.

Calculation of resultant force using force diagrams.

Application of resultant forces in different contexts, like a plane taking off.

Use of geometry to calculate resultant forces acting at angles.

Importance of the center of mass for stability in objects.

Practical demonstration of finding the center of mass using a plumb line.

Impact of the center of mass on the stability of vehicles like lorries.

Introduction to moments as the turning force around a fixed point.

Calculating moments with examples of a screwdriver and a crowbar.

Use of levers and moments in equilibrium situations, like a seesaw.

Explanation of gears and their role in altering speed and force.

Practical application of gear ratios in bicycles for different riding conditions.

Transcripts

[Music]

hi guys it's your science teacher here

back with another video this time

it's all about the first topic on

physics paper 2 which is forces

the topic starts off by looking at

scalar and vector quantities

scalar quantities just have size

whereas vector quantities have size

and direction some examples of some

scalar quantities could include

temperature mass

distance and speed

vector quantities also have a direction

and because they

often have direction they are often

forces

so assuming example of vectors are

weight

because you have to times the mass times

gravity so it's always going down

being attracted to the center of the

earth for weight

uh other vectors are displacement

which is the distance moved in a certain

direction

you also have acceleration

remember acceleration can be positive or

negative depending on which way you're

going

and also velocity

over here to represent the difference

between displacement and distance i've

drawn a house

and school now the distance from your

house to school

when you walk would be all the way that

this

road twists and turns okay so the

distance will actually be

a lot larger than the displacement

because the displacement is

just the distance from your house to the

school

whereas the distance you walk is all of

this

long weaving road so the displacement is

the distance moved in a certain

direction and that is why it's a vector

quantity and

distance is a scalar quantity a force is

a specific type of vector quantity

when one object puts a push

or a pull on another object

and forces can be broken down into two

categories

contact where the objects are touching

or non-contact

where the objects are not touching some

examples

of some non-contact forces when things

aren't touching can be

magnets you can see attraction and

repulsion

when you bring magnets close together

also

non-contact forces gravity you can't see

gravity but it's acting on us all the

time

it's not touching us but it's causing us

pull on

our bodies also we have

electrostatic forces as well which

happen inside atoms the positive

and negative charges in the nucleus

attracting

one another keeping that atom together

that's electrostatic attraction

we also have some more common forces

which are contact

forces such as air resistance

which occurs when you are

the air causes you to slow down air is

still particles it's not a non-contact

force

air has resistance inside it okay that

it

it stops you from moving so fast you see

it when you

you undergo terminal velocity that's

when

your gravity is equal to the air

resistance

another example of a contact force is

friction you experience friction

all the time even when you're just

walking think about it when you rub your

hands together your hands get extremely

warm that's

friction force acting just there any

driving force

that's contact think about it if you're

pushing off

something or you have a car engine the

force

of that that engine's put in that is

going to be a contact force because it's

going to be touching

newton came up with a law about forces

uh showing how uh objects interact with

each other

when a force is applied and this is

called newton's

third law of motion and newton's third

law

states that when an object

exerts a force on another object it

experiences

an equal

and opposite

force for example

if you've got a boxer and he punches a

punch bag it and he puts a hundred

newtons of

force onto that punch bag that punch bag

is gonna put a hundred newtons of force

back onto that boxes glove when it

touches it

up here i've got an example of a tractor

pulling a car

out of a mud and uh for the tractor to

be able to pull the car out of the mud

the force of the tractor on the car

needs to be greater than the car

on the tractor for it to move the equal

and opposite force here will be the

force of the tractor on the mud

being equal to the force of the mud on

the tractor

free body diagrams are used to look at

all the forces that act on a particular

object

for example if i was to look at a book

resting on a table it would have two

forces acting on it it will have

the weight of the book that's acting on

the table

and it will also have the force exerted

by the table on the book which keeps it

in the same position

and this is what's known as the normal

force

and the size of the arrows is important

they need to be exactly the same

size for keeping that book at rest

and this is known as newton's first

law

and unless we apply an external force

that book will stay at rest

however forces aren't always balanced we

know that because

nothing would accelerate or decelerate

if forces were completely balanced

for example let's look at a car for

example and we'll draw

all the forces acting on the car it has

the weight of the car going down

and it has the normal force of uh

the road acting back on it and these are

obviously the same

size okay because of the fact if the

weight force was

higher it would sink down and if the

normal force was higher

it would actually take off into the air

and it doesn't do that okay

um and it has other forces acting on it

as well it has

the uh driving force of the car pushing

it forwards

and it also has the friction

of the car acting backwards now if the

driving force

is exactly the same as the friction this

car will be moving at a constant speed

and we can actually use numbers to

represent the size

of the forces so we're going to use that

as well

so let's say this driving force is 5

newtons for it moving at a constant

speed

friction must also equal 5 newtons

now because the weight and the normal

force are going to be the same for all

these diagrams i'm not going to include

them

on uh the other two diagrams but they do

exist obviously um so let's look at an

accelerating car

now for a car to be accelerating the

driving force

needs to be larger than the friction

pulling it back this will cause

the car to accelerate for example if

this driving force was 15 newtons

this friction was two newtons that car

would be

accelerating

and we can actually quantify how much

that car will be accelerating

by a resultant force diagram now this

top one won't have a resultant force

because it's moving at a constant speed

however this one will okay and the

resultant force

would be 13 newtons this way

accelerating now what happens if the car

is not accelerating and it is

decelerating well it's just the opposite

okay that's where the friction

will be a lot larger than the driving

force going

forward uh for example if this was 15

newtons and this was 1 newtons of

driving force the resultant force would

be

14 newtons going that way and the car

would be decelerating

we know that the vertical component and

the horizontal component don't always

add

up for example if we look at a plane

taking off for example

that's going to have a resultant force

going upwards and a resultant force

going

forwards so if we were to look at um the

resultant forces

acting on this plane it might have a

resultant force in the vertical

plane of 120 newtons and a resultant

force in the horizontal plane

of 75 newtons if i draw

my diagrams to scale so it's moving

120 newtons upwards

and 75 newtons horizontally so

if we divide them by 10 it's easier to

work with with

a um ruler

so 7.5 centimeters in the horizontal

plane

and it will be moving 12 centimeters

in the vertical plane so if i keep that

as straight as possible it will make it

as

easy as it can be and then in order to

calculate the resultant force i need to

measure the distance between them

so if i draw my line on for the

resultant force

it is going uh 14.5

centimeters which would be a 145

newtons and you can actually measure the

angle

and give the angle of that the resultant

force is

acting when the forces don't act in the

vertical plane

or the horizontal plane uh we need to

use a

different tactic in order to work out

the resultant force vector

for example this is a ship here a big

ship

being pulled by two smaller ships

and both them smaller ships are at a 45

degree angle

to that ship now that will mean that it

was pulling

uh the ship in a uh

straight direction that's why they are

positioned there

and it will leave a resultant force

acting here

now working out how large that force is

we need to know the values of t1 and t2

work out tensions now they're going to

be the same if it's at the same angle

so if there's 2 000 newtons hanging out

there 2 000 newtons

hanging up here how can we work out how

big the resultant force is

pulling it forward well just like in the

last example where we used angles you

have to draw to scale diagrams

in order to make this work so you need

to measure the length

um of the t1 and t2 and make sure that

the same

size and then what you need to do is you

need to use your protractor and work out

where 45 degrees is

and then draw your lines going back in

to turn it into a parallelogram

then to work out the size of the

resultant force you just measure the

distance

here and because it's at the scale

diagram you will get the correct answer

for this example

it should be 4 000 newtons however it's

not

always 45 degrees that you'll be working

with

if it's smaller or larger you can get

smaller and larger resultant forces

you'll notice from my free body diagrams

i always draw

my forces acting from the center point

of

uh the object that i'm looking at for

example with the car

i picked the center point now i

shouldn't actually be doing that i

should be using something called the

center of

mass and this is uh the point

at which all the mass of an object can

be measured from

now for symmetrical objects it's really

easy to calculate the center of mass

because it's just the lines of symmetry

for example let's look at this

triangle here it has a line of symmetry

here

it has a line of symmetry here

and it has a line of symmetry here

now you can see that the centre of mass

of this object

will be here the same could be said for

this star okay if we draw the lines of

symmetry on the star

uh you've got a line here line here

line here and you've got

a line coming from here

and a light coming from here and you can

see

they all cross in the center which is

the center of mass

however not all objects are symmetrical

look at this object for example we can't

draw any

lines of symmetry on it instead we need

a

different way in order to calculate the

center of mass and the way we do that

is using the setup that we've got down

here you can see that i've drawn a clamp

stand

and the clamp stand is used with

something called

a plumb line and the plumb line acts

going completely down um

now what you need to do with your

objects you need to hang your object

from your clamp stand using a boss and

clamp

and pick a random point on the shape to

hang it then you use a ruler to draw

down

then you use a ruler to show where the

plumb line goes down

and you draw a line

then what you need to do is you need to

rotate your shape

and do this procedure again

and where the two lines meet will

the center of mass now center of mass

is extremely important for people to

know especially

if you are in the transport industry

because you want to make sure your cars

do not tipple over

and the center of mass needs to be quite

low um

for example if i looked at some lorries

if the center of mass

is exceeded for that lorry for example

if

the center of mass is here and it

tipples out onto the side and the center

of mass is outside the

object then that lorry will in fact

tipple over

so it's really important to know the

center of object mass

of objects in order to make them as

stable as possible

if you're doing gcse combined science

well done this is the end of the video

for you

if you are doing triple science uh just

a little bit more to go

we are now going to look at moments

levers and gears

how they work and why they work

what a moment is is it is the turning

force

of a uh around a fixed point some

examples of moments could be a door

opening or scissors acting around a

fixed point

or or even a spanner turning

a screw now the size of

the moment depends on two factors it

depends on the force

applied and the distance from

the pivot now the force for a

screwdriver for example

maybe i'm applying a force of 10 newtons

and this screwdriver could be 20

centimeters long in order to calculate

the

moment of that force i would have to do

10

newtons times 0.2 meters

remember moments will be measured in

newton meters

and this will give me a moment of

z to now a spanner is an example of a

lever same

with a crowbar because they can be used

in order to increase the amount of force

on an object

and if i was uh wanted to increase the

moment and increase

the pressure on that screw what i could

do is

lengthen my spanner or increase the

force that i put on it

here i've got another lever which could

be a crowbar

and my pivot would be here and

it works with exactly the same principle

as

a spanner does if a seesaw is

at rest you can calculate the distance

or the weight of a person by using

the fact that if it's at rest the

moment will be equal for each of them

for example if person a was sitting

here and they had a weight

of 60 newtons and

person b was sitting here

and they had a weight

of 80 newtons

and i knew the length uh from

person a to the pivot was

two meters i could now work out how

far away person b must be

for this system to be in uh equilibrium

so let's do that person a

is 2 times 60 newtons will give me

the moment there which is 120

newtons per meter

and that will equal 80 newtons

times the distance so that will tell me

that 120 newton

meters divided by 80 newtons will give

me the distance

which is 1.5 meters

and that's how to answer these moment

questions

uh they often like to use seesaws

around this pivot so you can calculate

the moment

for each of them people and you would be

able to calculate

either the weight or the distance that

that person

is away gears

also use the moment turning effect and

they work together to alter the speed

between

a driving mechanism and a driving part

if you are to look at these three gears

working together

you'll notice that the small one looks

like it's moving

faster that's because of the fact it

actually is okay

um the larger wheel has more

force but less speed whereas the smaller

wheel has

less force but moves quicker

this is why the smaller gear is at the

back of your bicycle and the larger gear

will be at the front of your bicycle

if you want to change your bicycle into

a higher gear

and make it harder for you to cycle you

will actually be selecting

a smaller gear on the back or a

larger one on the front that's because

of the fact the ratio between these two

sizes makes it more difficult

to cycle and turn the easiest gear to

move in

is when they are exactly the same size

they are in a one two one ratio and this

is what is used when you're going up

steep hills you want the chains at the

cogs to be the same size and this will

mean that it's easier to

cycle now i hope you've enjoyed watching

the video please remember if you did to

like the video and also subscribe to

my channel