Work & Power How the world works….

Define / Describe WORK Work is done when a force causes an object to move in the direction that the force is applied. The formula for work is: W = F X D If there is no movement, there is no work

Work or Not?

Joules? Work is measured in Joules. Rule for Work Work (Joules) = Force (Newtons) X Distance(meters) W = F X d Example to calculate Work Question: A weightlifter raises weights of 2000 Newtons from the floor to a height of 2 meters. How much work has been done? Answer: W = F X d W = 2000 X 2 W = 4000 Joules

What is Energy? Energy - ability to cause change; can change the speed, direction, shape, or temperature of an object

What is Power? Power is the rate at which work is done. Power is measured in Watts. Rule for Power Power (Watts) = Work (Joules) / Time (seconds) P = W / T Example of calculating Power Question: A weightlifter lifted 2000 Newtons to a height of 2 meters. What is the power output if this was done in 2 seconds? Answer: P = W / T = 4000 / 2 = 2000 Watts

work w F d POWER time Work is measured in Joules (J) Power is measured in Joules/second or Watts

How much work is done when an 8N force moves a block 7m?

Eva applies 40N force to move her bookcase 3m, how much work did Eva do?

How far will 490J of work raise a block weighing 7N?

Which is more work, pushing with 115N over 15m or lifting 20N over 10m?

How much power does it take to do 500J of work in 10 sec?

How much power does it take to lift 250N, 40 m high in 2 sec?

If it takes 20N to move a box, how much power will be needed to move the box a distance of 5 meters in 5 sec?

Calculate the power expended when a 500N barbell is lifted 2 Calculate the power expended when a 500N barbell is lifted 2.2 m in 2 sec.

A 190,000 W engine can accelerate from rest to a top speed in 9sec A 190,000 W engine can accelerate from rest to a top speed in 9sec. How much work did the engine do?

If a runner exerts 350J of work make 125 W of power, then how long did it take the runner to do the work?

Challenge Question An escalator is used to move 20 passengers every minute from the first floor of a department store to the second floor. The second floor is located 5 meters above the first floor. The average passenger’s mass is 60 kg. Determine the power requirements of the escalator in order to move this number of passengers in the amount of time.

Three things must happen for work to be done. A force must applied to an object The object must move The motion must be in the same direction in which the force is being applied.

What is purpose of a machine? To make work easier.

How do machines make work easier? Any change in the size of the force changes the distance. No machine can increase both force and distance. Multiply force which decreases distance the load moves. Multiply the distance which decreases force. Or, they leave force and distance alone but change the direction in which the load moves.

How do machines make work easier? They can change the amount of force They can change the distance (Remember that Work = Force X Distance) They can also change the direction MORE

What is mechanical advantage? The number of times a machine multiplies the effort force.

What are the 3 types of simple machines? There are three simple machines: the lever, the pulley, and the inclined plane The wheel and axle, the wedge, and the screw are modifications of the three simple machines.

What is a compound (or complex) machine? A machine made up of two or more simple machines.

Works Cited Notes were adapted from The Science Class web site at www.science-class.net and from Queensland Science Teachers at http://qldscienceteachers.tripod.com/junior/physics/work.html