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Hold down the T key for 3 seconds to activate the audio accessibility mode, at which point you can click the K key to pause and resume audio. Useful for the Check Your Understanding and See Answers.

LOL Charts (a.k.a., Energy Bar Charts) - help5

The total energy in the universe is constant. Energy can be transformed from one form to another or transferred from the system to the surroundings (or vice versa), but in the end the total amount of this energy remains the same. A bar chart is a useful tool for illustrating how energy is stored, transferred, and conserved.

There are two similar versions of this question. Here is one of those versions:

Version 1:
Initial State: Car at rest at top of a hill.
Final State: Car in motion at about the half-way point to the bottom of the hill.
Notes: The system includes the car and earth. Resistance forces are negligible. The car coasts while in neutral.
System: Car-Earth

As mentioned in the Fundamentals section above, positive work occurs when the force acts in the same direction as the motion of the object. And negative work occurs when the force acts opposite the motion of the object. So think of the object in this situation and try to imagine which direction the force must be acting in order for the object to move in the manner that it is described as moving. Ask: how does the direction of the force compare to the direction of the motion? Is it in the same direction or the opposite direction as the motion?

If the above paragraph doesn't help, then try the following:
Positive work increases the total mechanical energy of the object. One would observe a speeding up (increasing KE) or an increasing height (increasing PE) or both. And negative work decreases the total mechanical energy of the object. One would observe a slowing down (decreasing KE) or a decreasing height (decreasing PE) or both. So read the description carefully and try to determine if the work is causing the object to gain mechanical energy or lose mechanical energy.

There's a lot of concepts in this Concept Builder. Most are covered at The Physics Classroom Tutorial:

Kinetic Energy

Potential Energy

Bar Chart Illustrations