Lesson 2.2: Lever Investigation

This investigation is easy to do anywhere-at home or in school.

What You Need

  • 30 cm ruler (You may use a thin board such as a paint stirstick if you do not have a 30 cm ruler, but you will have to measure the distances using a measuring tape or a small ruler)

  • pencil or a pen-not a round one but one that has a hexagonal shape (6 flat edges)

  • 4 pennies (Try to get all with the same year so that they will have the same mass.)

What To Do

  • Print the following table or make a copy in your notebook.

Situation (Balanced)

Left Reading (cm)

Centre Reading (cm)

Right Reading (cm)

Example

29.6 cm

16.5 cm

 3.3 cm

One penny on each side

     

One penny on the left side and two on the right side

     

One penny on the left side and three on the right side

     

 

  • Balance the ruler on your pencil as shown below.

  • Read and record the point on the ruler that is in the middle of the pencil.  Note that this may not be the 15 cm mark.  The ruler may have a hole in one end or just might be heavier at one end than the other.  This does not matter, the important thing is that you have the middle point of the balanced ruler.  The distances are calculated from this point.

  • Place one penny at one end of the ruler and one penny at the other end of the ruler.  Be sure the ruler is not moving from its centre point.

  • Move one of the pennies until the ruler balances.  Read and record the the ruler value for the centre of each penny.

  • Add another penny on top of the penny on the right-hand side of the ruler.  Move the two pennies until the ruler balances.  Read and record the the ruler value for the centre of the two penny pile.

  • Add another penny on top of the two penny pile on the right-hand side of the ruler.  Move the three pennies until the ruler balances.  Read and record the ruler value for the centre of three penny pile.

Analyze

  • For each of the situations, calculate the difference between the left reading and the centre reading.

  • For each of the situations, calculate the difference between the right reading and the centre reading.

Situation (Balanced)

Left Reading -
Centre Reading

Right Reading -
Centre Reading

Example

29.6 cm - 16.5 cm = 13.1 cm

16.5 cm - 3.3 cm = 13.2 cm

One penny on each side

   

One penny on the left side and two on the right side

   

One penny on the left side and three on the right side

   


A penny has a mass of about 2.5 g.  Complete the following table by multiplying the mass of the coin(s) on each side by the distance from the coin(s) to the centre (fulcrum).  Note that you already found the distances by subtracting the left and right readings from the centre reading and entered them in your table.

Situation (Balanced)

Left Side
Mass ? Distance

Right Side
Mass ? Distance

Example

2.5 g ? 13.1 cm = 32.75 g·cm

2.5 g ? 13.2 cm = 33 g·cm

One penny on each side

   

One penny on the left side and two on the right side

   

One penny on the left side and three on the right side

   

Question 1. What is the relationship between the mass times the distance on the left side and the mass times the distance on the right side for each situation?

 

Check your answers with those that follow.

 

 

 

 

 

 

 

 

 

 

 

Answers to Questions:

Question 1. What is the relationship between the mass times the distance on the left side and the mass times the distance on the right side for each situation?

The product of mass times distance should be the same on the left side as it is on the right side.  Because this is an experiment, you may have values that are slightly off, as is evident in the example.  32.75 g·cm is very close to 33 g·cm.  This is a very important concept used in the next lessons.

For a balanced lever,

Load ? Load distance = Effort ? Effort Distance

 


Click on the page forward to continue Lesson 2.