University of Virginia
Physics Department

Levers

A Physical Science Activity

Student Activity

Materials
  • 2 Spring scales (10 N or 1 kg maximum)
  • Gravel or Sand (240 g) to fill plastic bottle
  • 3 Rubber bands, medium size
  • Plastic spoons
  • ½ meter stick or ruler
  • Water to fill excess space in plastic bottle
  • Binder clip, medium
  • Triple beam balance or digital scale
  • Dowel, at least 25 cm long, 0.5 cm diameter
  • Masking tape (one inch wide)
  • Pencil eraser, wedge-shaped, to fit on end of dowel
  • Black ball point pen
  • Plastic bottle with screw eye in lid (250 mL)--can be ordered from Delta Education Catalog (1-800-258-1302); item number 420211232

 

Procedure

  1. Fill the plastic bottle with gravel. Mass it using the balance. If the mass is less than 240 g, add water to increase the mass.
  2. Attach one rubber band to the screw eye of the bottle and one to the top hook of the spring scale. This will allow the bottle and scale to hang from the ruler.
  3. Cover the inch measurements on the ruler with masking tape. Using a meter stick or a second ruler to measure, mark increments of 5 cm along the masking tape from end to end.
  4. Secure the dowel rod to a desk or table top with masking tape and possibly a book or other heavy object.
  5. Clip the binder clip to the midpoint of the ruler from the bottom side. Flip up the metal clips, so that they curve down. Slide this loop onto the dowel rod.
  6. Attach the eraser to the end of the dowel rod, so that the binder clip cannot slide off.
  7. To measure the force of the spring scale itself, attach one spring scale to the bottom of another. Read the measurement off of the top scale, and record it in the data sheet.
  8. Hang the load from the spring scale and record the amount of force that is required to lift it without the lever.
  9. Hang the load on the lever arm, 10 cm from the fulcrum (binder clip). Attach the spring scale to the opposite end of the lever arm, 2.5 cm from the fulcrum. Pull down on the spring scale to raise the load until the lever arm is parallel to the surface. Record the required force on the data sheet.
  10. Repeat step 9 with the spring scale at five more locations: 5 cm, 10 cm, 15 cm, 20 cm, and 25 cm from the fulcrum. Record the results on the data sheet.

 

Data Sheet

Spring Scale Force Alone (N)

Position of Effort (mass)

Effort Reading (N)

Total Effort (Reading + Spring Scale Force) (N)

2.5 cm

 

 

5 cm

 

 

10 cm

 

 

15 cm

 

 

20 cm

 

 

25 cm

 

 

Questions

1. Plot your results on graph paper. Label the x-axis for distance from the fulcrum by units of centimeters. Label the y-axis as total effort in newtons. (Your graph should resemble the example below) Connect the data points to make a curve. Use this plot to answer the following questions.

 

2. How much force would be required to lift the load (at 10 cm) if the effort were 13 cm from the fulcrum?

 

 

3. If 7.5 N of force were required to lift the load, how far from the fulcrum was the effort?

 

 

4. If the load were placed 20 cm from the fulcrum instead of 10 cm, how would your data change? Would your curve look any different? Explain.

 

 

5. Give three examples of levers that you could find in your home or school. Identify the effort, load and fulcrum.