Inclined Planes, Work, Mechanical Advantage and Efficiency
In this lab, you will explore work and mechanical advantage of an inclined plane. Machines help us do
work by multiplying the force that we apply or by changing the direction of the force. Inclined planes
multiply our applied force.
The amount by which a machine can multiply a force is called the machine’s Mechanical Advantage.
Whether a machine is useful depends on whether it gives us more mechanical advantage than doing the
work ourselves. For example, can we raise a large number of concrete blocks up in the air better with
a machine? If so, then it is useful and has an advantage of some value times more than if we did it
ourselves.
Mechanical Advantage is the ratio of force output (the weight of the object) to force input (the
reading on the spring scale). Since both forces are in Newtons, the unit cancels out.
MA = FO
Force Output is the weight of the box.
FI
Force Input is the spring scale reading.
Efficiency is the percentage of input work that is converted to usable output work. Work output is
defined, in this case, as the Weight of the object x the height it is lifted.
Work input is defined, in this case, as the Spring Scale Reading x the length of the incline.
Efficiency = Work Output
Work Input
Purpose: To calculate the amount of work (W = F x d) done by you and the machine and then
determine the mechanical advantage and effeciency of a simple machine.
Materials: Inclined plane, wooden box, pulley, meter stick, hanging masses, protractor
Procedures:
1. Measure the length of the inclined plane. Record.
2. Measure the mass of the wooden box. Record. Place 300 g into the box. Record the total mass.
3. Fix the inclined plane so that the very top of the incline is 10 cm above the lab table.
4. Place the wooden box at the bottom of the incline and attach the spring scale to the box. Using the
spring scale, pull the box up the incline at constant velocity. Record the reading on the scale.
5. Increase the height of the incline to 20 cm. Repeat Step 4.
6. Increase the height of the incline to 30 cm. Repeat Step 4.
7. Increase the height of the incline to 40 cm. Repeat Step 4.
NAME ________________________ PARTNER ___________________ DATE ________
DATA TABLE
Length ______
Mass of Wooden Box ________
Mass of box + 300 g _________
Height (in meters)
Force (Spring Scale Reading)
0.10 m
0.20 m
0.30 m
0.40 m
Calculations:
1. Convert the mass of the wooden box plus the 300 g to kilograms
2. Determine the weight of the wooden box and weight using the answer from 1. ( Fw = m g; where m
is in kg and g is 9.8 m/s2.)
3. Determine the mechanical advantage of the machine at each height.
4. Calculate the amount of work done by the machine for each trial. (OUTPUT WORK)
5. Calculate the amount of work done by you for each trial. (INPUT WORK)
6. Determine the efficiency of the machine at each height.
7. What conclusions can you make about the angle of the incline and its mechanical advantage?
CALCULATIONS TABLE
Weight of the wooden box plus 300 g
Height
Mechanical
Advantage
0.10 m
0.20 m
0.30 m
0.40 m
Show your calculation here:
_____________
Output Work
Input Work
Efficiency
Post- Lab
1. What is mechanical advantage?
2. What are the two ways that a machine can help us do work?
3. A student pushes a box a distance of 3.5 m using a force of 15.5 N. How much work has the
student done?
4. 300 j of work is done to lift a box 1.5 m. Determine the amount of force used.
5. A person weighing 300 N climbs a tree to rescue a cat who is afraid to jump 8.0 m to the ground.
How much work is done by the person to rescue the cat?
6. Two movers must load a dryer onto a truck. They use an inclined plane that is 4.3 m long and
exert a total force of 250 N. The bed of the truck is 1.3 m above the ground and the dryer weighs 800
N. Determine the mechanical advantage of the inclined plane.