Science Starter!

Discuss and write a response to the following:

Define “work”.

Work, Power and Energy

Work Done by a Constant ForceThe work done by a constant force is defined as the distance moved multiplied by the component of the force in the direction of displacement:

The units of work are: Joules (J)

Work Done by a Constant Force

Be careful:

As long as this person does not lift or lower the bag of

groceries, he is doing no work on it. The force he exerts has no component in the direction

of motion.

Example 11. How much work is done by pulling a

25 kg box for 6 m with 50 N of force?

2. How much work would be done if the handle made an angle of 30° to the ground?

 1. 2.

Work and EnergyWhen work is done, energy is lost (or gained).

Familiar Units of work/energy:

1 cal = 4.184 J

1 kcal = 1 Calorie = 4,184 J

Example 2

 

1. How many calories are expended in Question 1 from Example 1? Calories?

Work Done by a Varying Force

For a force that varies, the work done is the area under the force vs. distance curve.

PowerPower is the rate at which work is done:

The difference between walking and running up these stairs is power – the work done is the same.

The units of power are Watts.

Example 3

(a)How much work does a 55 kg student do in climbing a 4 m tall staircase?

(b) How many Calories does the student expend?

(c) How much power does the student generate if he reaches the top in 2.5 seconds?

 

 

(a)

(b)

(c)

 

Electrical Energy

 

Harnessing Human Power