1. Work, Mechanical Advantage & Weight Review

2. What is Work?
Work=product of the force applied and the distance the object moves.
Two factors that affect work:
Force
Distance
An object has to move in order for work to be done.

3. Calculating Work Work=Joules (J) Force=Newtons (N) Distance=Meters (m)
Formula:
Units:
Work=Joules (J)
Force=Newtons (N)
Distance=Meters (m)

4. Using the Work Formula
A worker uses a cart to move a load of bricks 10 m across a parking lot. If he pushes the cart with a constant force of 209 N, what amount of work does he do?

5. Using the Work Formula
A weight lifter produces 3,750 Joules of work to raise a 1500 Newton barbell. How far did he lift the barbell?

6. Using the Work Formula
A construction worker did 96J of work moving a steel beam 6.4 meters across a construction site. How much force was used to move the steel beam?

7. What is Mechanical Advantage?
The number of times that a machine multiplies the effort force.
Mechanical advantage does not have a unit that goes with the number value.

8. Important Vocabulary
Effort force (N) – this is the force that the user puts into a machine (input).
Resistance force (N) – this is the force that the machine provides as an output force.
Effort distance (m or other distance units) – this is the distance that is the put in to the machine by the user (input).
Resistance distance (m or other distance units) – this is the distance that the machine moves something (output).

9. EFFORT=YOU
RESISTANCE=MACHINE

10. Calculating Mechanical Advantage
Use this formula when given distances (m, etc.) in machines.
Mechanical Advantage = effort distance
resistance distance
Use this formula when given forces (N) in machines.
Mechanical Advantage = resistance force
effort force

11. Using the Mechanical Advantage Formulas
Determine the mechanical advantage of a machine when you exert 23 N of effort force and the machine produces 115 N of resistance force.

12. Using the Mechanical Advantage Formulas
Calculate the MA of a ramp that is 2 meters high and is 15 meters across the slope.

13. Using the Mechanical Advantage Formulas
What is the mechanical advantage of the pulley system in the picture?

14. The measure of the force of gravity on an object.
What is Weight?
The measure of the force of gravity on an object.

15. Weight vs. Mass Weight is affected by gravity.
The weight of an object will change depending on the amount of gravity acting on it.
Weight is measured in Newtons (N).
The weight of an object is determined using a spring scale.
Mass is not affected by gravity.
Mass remains the same.
Mass is measured in kilograms (kg).
The mass of an object is determined using a triple beam balance.

16. Calculating Weight Formula: Weight=mass X acceleration due to gravity
W=mg
Units:
Weight=Newtons (N)
Mass=Kilograms (kg)
Gravity=9.8 m/s2 on Earth
**The amount of gravity will be different depending on where the object is, for example on Earth, on the moon or on another planet.**

17. Using the Weight Formula
What is the weight of a boy who has a mass of 42 kg (gravity on earth is 9.8m/s2)?

18. Using the Weight Formula
The gravity on Jupiter is m/s2. Determine the weight of a space rover that has a mass of 15 kg.

19. Objects Affecting a Falling Object
Gravity pulls down on a falling object. Air resistance pushes up on a falling object.
Gravity accelerates a falling object. Air resistance slows a falling object.
Objects with a greater surface area fall at a slower rate.
Mass has little affect on falling objects.
**AIR RESISTANCE IS THE MAJOR FACTOR THAT AFFECTS THE RATE AT WHICH AN OBJECT FALLS.**