Have you done any work today? Work: (W) the transfer of energy that occurs when a force makes an object move. Measured in Joules Two conditions must be met: Object must move Force must be applied in the direction of the movement. I love to start off asking this question, and to see what THEIR definitions of work are before I share with them the physics definition of work. The picture included only depicts work being done IF the person is moving the books, not just standing still.

Can be summarized as an equation. Work Can be summarized as an equation. W = Fd W = work Measured in J F = force Measured in N d = distance Measured in m Example #1: You move a 75 kg refrigerator 35 m. This requires a force of 90 N. How much work, in joules, was done while moving the refrigerator? m = 75 kg d = 35 m F = 90 N W = ? W = (90)(35) W = 3,150 J W = Fd

Practice Time A book weighing 1 N is lifted 2 m. How much work was done? A 1 kg book is lifted 2 m. How much work was done? 250 J of work are needed to push a box up a ramp. The force needed to push the box up the ramp is 10 N. How far up the ramp was the box pushed? If 56 J of work energy is required to lift a dumbbell to a height of 7 m, what is the weight of the dumbbell? Answer: W = 2 J Answer: W = 19.6 J I have students work these out in their notes and I walk around and help them as they work. Then we go over the answers all together. I especially encourage CP students that if they don’t know what to do, they at least need to set up the problem (labeling values that they know and writing the appropriate equation.) They should NEVER leave a problem blank! # 2 students may need help realizing they can always find Force if they have mass because they can use ag = 9.8 m/s2 to find weight! Answer: d = 25 m Answer: w = F = 8 N

Power Power: (P) the amount of work done in a certain time; the rate at which work is done. P = W t P = power Measured in J/s Or Watts = W W = work Measured in J t = time Measured in s

Example #2 It took 150 seconds to move a refrigerator. You did 3,150 joules of work in the process. How much power was required to move the refrigerator? t = 150 s W = 3,150 J P = ? P = 3150 150 P = 21 J/s or 21 Watts P = W t