: Simple Machines

Physical Science

• With your partner (on the back of your study guide),

identify the 6 different simple machines and give 1 example of each which can be seen in this classroom or somewhere in the

school.

• A simple machine is a device which does work (w = f x d) with only 1 movement.

• Simple machines make work easier by

• There are 6 different simple machines.

1. Lever

2. Pulley

3. Wheel & Axle

4. Incline Plane

5. Wedge

• If 2 people are pushing identical boxes the exact same distance, then they are doing the same amount of work (F x D).

However, if one is pushing the box faster than the other, then that person is

generating more power.

• The formula for power is:

Power = Work / Time

• Let’s say Gary is lifting weights at the gym. It takes him 2 sec. to lift a 120 N weight over his head (0.5 m).

• How much work did Gary do?

• A compound machine is a combination of 2 or more simple machines working

• The force put into a machine to do the

work is called the effort force. That is what you apply.

• The force then produced by the machine is called the resistance force.

• So the hand is applying the effort force, and the resulting force which lifts the rock is the

• Sometimes, a machine can actually produce more force than you put into it. That’s how you might be able to lift a person on the

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

M.A. = F

/ F

• “Give me a lever long enough and I could move the world”

• For example:

Bud weighs 100 N. So when he sits on the teeter totter he is applying a force of 100 N (F_e). He is able to lift Mike and Gary who have a combined weight of 150 N. Therefore, 150N would be the resistance force produced by the teeter totter (F_r).

• There are 3 parts to a lever: 1. Axis

2. Effort arm - where the F_e is applied

3. Resistance arm - where the F_r is applied



• There are also 3 different classes of

levers. 1st class, 2nd class, and 3rd class.

Work

& Work

• Work is F x D. The amount of work you put into a machine (work_in) is determined by the effort force which you apply, and the

distance over which you apply it.

• For example, if the lever below is pushed downward 2 m with 50 N of force, then

• Likewise, work

is equal to the

resistance force times the

distance which it is moved

(resistance distance).

• So in the same lever below, Work_out = 25 N x 4 m

• If the amount of work put into a

machine is equal to the amount of

work which comes out of the

machine, then it is said to be an ideal

machine.

• However, when a simple machine is used, often times friction will come into effect. • For example, if you are using a wheel and

• As a result, you may need to put more work into the machine to get a certain amount out.

• The ratio of work in to work out is called efficiency.

• Answer:

Efficiency = W_out / W_in

• A pulley does 500 J of work to lift a 125 N

Answers:

• Work = Force x Distance

so, Distance = Work / Force

1. A rusty pulley has an efficiency of .25. If a person does 400 J of work to lift an

object, how much work will be done by the machine?

2. If the person in question #1 does the

work in 8 sec., how much power did the person produce?

4. A kid on a teeter-totter does 800 J of work as he lifts another kid 1 m upward. If the other kid had a weight (Fr) of 600 N, what is the efficiency of the teeter-totter?

5. A crane lifts a 35,000 N steel girder a distance of 25 m in 45 sec. How much

work was done, and how much power did the crane require to lift the girder?

Kim and Chris want to teeter totter together. However, Chris weighs 25

pounds more than Kim. If Chris sits 2 m away from the axis on her side of the

teeter totter, will Kim need to sit the same distance away, closer to the axis, or

• On a typical trebuchet, the resistance arm (projectile side) is longer than the effort arm (counter-weight

side). However, if the effort arm were made longer and the resistance arm shorter, that would increase the amount of effort force put into the machine.

• Identify 4 simple machines used in the Goldberg

• Come up with 1 completely new

Subject #

Weight

(lbs) Weight (N)

Distance

Traveled Time (1) Time (2)

Average Time

1

2

3

1. How much work was done by each of the subjects? (Show work!)

Subject 1 _________ Subject 2 _________ Subject 3 _________

2. How much power was produced by each of the subjects? (Show work!)

Subject 1 _________ Subject 2 _________ Subject 3 _________

3. Did the person who made it up the stairs the quickest produce the most power? Why or why not?

4. Do you see any relationship between the size of the person and the amount of work done? If so, what is that relationship?