Work as the transfer of energy | Work and energy | Physics | Khan Academy
Summary
TLDRThe script explains the concept of work done through the formula Fd cos(theta), highlighting its relation to energy transfer. It illustrates positive work with a skateboarder gaining kinetic energy and negative work with the skateboarder losing energy upon crashing. The script further clarifies the principle using gravitational potential energy, showing how lifting bricks results in positive work done. It concludes by emphasizing that work can be determined by the energy an object gains or loses, applicable to all forms of energy.
Takeaways
- đ The formula for work done is Fd*cosine(theta), which represents the energy transferred to an object.
- đ Positive work done (+200 joules) means the force gives energy to an object.
- đ Negative work done (-200 joules) signifies the force takes energy away from an object.
- đŽ An example is a 50-kilogram skateboarder who gains 2,500 joules of kinetic energy when moved by a force.
- đïžââïž The skateboarder's kinetic energy is the measure of the positive work done by the force.
- đ„ When the skateboarder crashes into a stack of bricks, the bricks do negative work by removing energy.
- 𧱠The work done by the bricks is calculated by the energy they took away from the skateboarder.
- đ Lifting bricks upwards transfers energy to them in the form of gravitational potential energy.
- đ Gravitational potential energy is calculated using the formula mgh, where m is mass, g is acceleration due to gravity, and h is height.
- đ The concept of work done applies to all types of energy, not just kinetic and potential energy.
Q & A
What is the formula used to calculate the amount of work done?
-The formula used to calculate the amount of work done is Fd cosine theta.
How does the amount of work done relate to energy transfer?
-The amount of work done represents the amount of energy transferred to an object.
What does a positive value of work done indicate?
-A positive value of work done indicates that the force gave energy to the object.
How much kinetic energy did the skateboarder gain when moving at 10 meters per second?
-The skateboarder gained 2,500 joules of kinetic energy.
What is the relationship between force and work when the skateboarder crashes into a stack of bricks?
-The stack of bricks does negative work on the skateboarder because it takes away energy from the skateboarder.
How much work is done by the bricks on the skateboarder when they come to a stop?
-The work done by the bricks on the skateboarder is negative 2,500 joules.
What type of energy is gained by the bricks when they are lifted upwards?
-The bricks gain gravitational potential energy when they are lifted upwards.
What is the formula to calculate gravitational potential energy?
-The formula to calculate gravitational potential energy is mgh.
How much gravitational potential energy did the 500-kilogram bricks gain when lifted four meters?
-The bricks gained 19,600 joules of gravitational potential energy.
What does it mean when a force gives energy to an object?
-When a force gives energy to an object, it is doing positive work on that object.
Can the concept of work done be applied to all types of energy?
-Yes, the concept of work done can be applied to all types of energy, not just gravitational potential energy and kinetic energy.
Outlines
đ§ Understanding Work Done Through Energy Transfer
This paragraph explains the concept of work done using the formula Fd cos(theta), which represents the energy transferred to an object. It illustrates the idea with the example of a skateboarder gaining kinetic energy from a force that starts their motion, resulting in positive work done. Conversely, when the skateboarder crashes into a stack of bricks, the bricks do negative work by taking away energy. The paragraph also discusses how to find work done by considering the change in energy, such as gravitational potential energy gained by lifting bricks.
Mindmap
Keywords
đĄWork Done
đĄEnergy Transfer
đĄKinetic Energy
đĄGravitational Potential Energy
đĄPositive Work
đĄNegative Work
đĄDisplacement
đĄForce
đĄCosine Theta
đĄAngle of Force
đĄEnergy Conservation
Highlights
Work done can be calculated using the formula Fd cosine theta.
Work done represents the energy transferred to an object.
Positive work done indicates energy given to an object.
Negative work done indicates energy taken away from an object.
Determining energy gain or loss can provide an alternate way to find work done.
Example of a skateboarder gaining kinetic energy from a force.
The skateboarder's kinetic energy gain is 2,500 joules.
Work done by the force on the skateboarder is positive 2,500 joules.
Force doing positive work gives energy to an object.
Force doing negative work takes away energy from an object.
Example of a skateboarder losing kinetic energy upon crashing into bricks.
The bricks do negative work by taking away the skateboarder's energy.
Work done by the bricks is negative 2,500 joules.
Lifting bricks upwards gives them gravitational potential energy.
Gravitational potential energy is calculated using the formula mgh.
The bricks gain 19,600 joules of gravitational potential energy.
Work done on the bricks is positive 19,600 joules.
The concept of work done applies to all types of energy.
Work done by a force can always be found by determining the energy given or taken away.
Transcripts
One way to find the amount of work done
is by using the formula Fd cosine theta.
But this number for the amount of work done
represents the amount of energy transferred to an object.
For instance, if you solve for the work done
and you get positive 200 joules, it
means that the force gave something 200 joules of energy.
So if you have a way of determining
the amount of energy that something gains or loses,
then you have an alternate way of finding the work done,
since the work done on an object is the amount of energy
it gains or loses.
For instance, imagine a 50-kilogram skateboarder
that starts at rest.
If a force starts the skateboarder moving
at 10 meters per second, that force
did work on the skateboarder since it gave the skateboarder
energy.
The amount of kinetic energy gained by the skateboarder
is 2,500 joules.
That means that the work done by the force on the skateboarder
was positive 2,500 joules.
It's positive because the force on the skateboarder
gave the skateboarder 2,500 joules.
If a force gives energy to an object,
then the force is doing positive work on that object.
And if a force takes away energy from an object,
the force is doing negative work on that object.
Now imagine that the skateboarder, who's
moving with 10 meters per second,
gets stopped because he crashes into a stack of bricks.
The stack of bricks does negative work
on the skateboarder because it takes away energy
from the skateboarder.
To find the work done by the stack of bricks,
we just need to figure out how much energy it took away
from the skateboarder.
Since the skateboarder started with 2,500 joules
of kinetic energy and ends with zero joules of kinetic energy,
it means that the work done by the bricks on the skateboarder
was negative 2,500 joules.
It's negative because the bricks took away energy
from the skateboarder.
Let's say we instead lift the bricks, which
are 500 kilograms, upwards a distance of four meters.
To find the work that we've done on the bricks,
we could use Fd cosine theta.
But we don't have to.
We could just figure out the amount of energy
that we've given to the bricks.
The bricks gain energy here.
And they're gaining gravitational potential energy,
which is given by the formula mgh.
If we solve, we get that the bricks
gained 19,600 joules of gravitational potential energy.
That means that the work we did on the bricks
was positive 19,600 joules.
It's positive because our force gave the bricks energy.
This idea doesn't just work with gravitational potential energy
and kinetic energy.
It works for every kind of energy.
You can always find the work done by a force on an object
if you could determine the energy that that force gives
or takes away from that object.
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