We’ll cover power in a little bit, but first we need to have a unit of measurement for work. The units for work and energy are the same, but note that energy and work are not the same. (Remember, energy is the ability to do work.)


For energy, a couple of units are the Joule (J) and the calorie (cal or Cal). A Joule is the energy needed to lift one Newton one meter. A Newton is a unit of force. One Newton is about the amount of force it takes to lift 100 grams or 4 ounces or an apple.


It takes about 66 Newtons to lift a 15-pound bowling ball and it would take a 250-pound linebacker about 1000 Newtons to lift himself up the stairs! So, if you lifted an apple one meter (about 3 feet) into the air you would have exerted one Joule of energy to do it.


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2 Responses to “Units for Energy”

  1. Work is the energy transferred to or from an object by applying force along a displacement. Since gravity is “up and down”, if the force is moving perpendicular to the Earth’s gravitational field (gravity does not make objects slide sideways), then there is no work done against the gravitational field. The next lesson is “moving against a force” and that should help explain this idea further.

    It’s important to know the difference between conservative and non-conservative forces. The work done by a conservative force is path-independent, meaning that the actual path that the object takes makes no difference. Fifty feet up in the air has the same gravitational potential energy whether you get there by climbing a ladder or or by hopping on a helicopter.

    It is different from the force of friction, which transforms kinetic (moving) energy to heat. When friction is involved, the path you take does matter, because if the path is longer, then more energy is transferred to heat. so friction is a non-conservative force. Air resistance is another non-conservative force.

    So for the example in the video, the work done against the gravitational force is zero, since we did not move it “up or down” in the same direction as gravity pulls. We did not look at frictional forces yet. Does that help?

  2. Could you please clarify how the rock moves if total work is equal to zero?