It might be better to call potential energy "positional energy" since it is the energy a body has due to its position.
Consider lifting a pen from the floor to your desk. The overall change in potential energy is unrelated to the path you took, whether direct or loopy.
Key Concepts
Work is done on a body to lift it at constant velocity. Work done = force x distance:
\(F=Wh=mgh\)
Remember when something is lifted at constant velocity the forces are balanced. No kinetic energy is gained.
A common mistake is to think that 'mgh' is the general equation for Ep. However, this only applies close to the Earth (where the gravitational field is uniform).
The gravitational field of the Earth is only uniform close to it. If we take a spacecraft away from the Earth, gravitational field strength will decrease. This means that the work done to increase the distance per metre will also decrease.
The area under a work done - distance graph gives the potential energy change.
Use quizzes to practise application of theory.
START QUIZ!
A 10 kg ball is lifted to a height of 3 m at constant velocity.
The change in potential energy of the ball is:
PE = mgh
PE increases as work is done on the ball
A 10 kg ball is lifted by a 200 N force to a height of 5 m.
The work done on the ball is:
Work done = Force x distance
This is greater than the increase in PE so the ball will also have KE
10 J of work are required to move a charge of 10 μC from A to B along the path shown.
The change in PE is
Don't be put off by the fact that this is about electric charges. Change of PE is equal to the work done going from A to B.
A 5 kg box is carried up the slope shown at a constant speed.
The work done on the box is:
Work done = increase in PE = mgh = 5 x 10 x 300
How much of Potential energy have you understood?
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