P8 - WHOLE TOPIC GCSE FORCES
Summary
TLDRThis 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
- đą Scalar quantities have only magnitude, like temperature, mass, distance, and speed.
- đ§ Vector quantities have both magnitude and direction, such as weight, displacement, acceleration, and velocity.
- đ Weight is a vector quantity because it always pulls downward due to gravity.
- đ 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.
- đ€Č Forces can be contact forces, like friction, or non-contact forces, like gravity and magnetic forces.
- đ§Č Non-contact forces include magnetic attraction/repulsion, gravity, and electrostatic forces within atoms.
- đ Newton's third law of motion states that for every action, there is an equal and opposite reaction.
- đ Free body diagrams are used to visualize all the forces acting on an object, such as weight and normal force.
- đ Forces can cause objects to accelerate or decelerate; the resultant force is the net force acting on an object.
- đ Resultant forces can act in different directions, like a plane taking off, which has both upward and forward forces.
- đ 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
đŹ 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.
đ 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.
đą 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.
đ§ 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.
đŽââïž 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.
Mindmap
Keywords
đĄScalar Quantities
đĄVector Quantities
đĄDisplacement
đĄForce
đĄContact Forces
đĄNon-Contact Forces
đĄNewton's Third Law of Motion
đĄFree Body Diagrams
đĄResultant Force
đĄCenter of Mass
đĄMoment
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
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