TO VERIFY THE PRINCIPLE OF CONSERVATION OF MOMENTUM

APPARATUS

Linear air-track, blower, two gliders, small card, blue tack, two light gates, timer, electronic balance, spirit level, ruler.

METHOD

Set up the linear air track , blower, light gates and timer as in diagram.
Ensure the track is horizontal, checking with the spirit level.
Find the mass, m₁, of the first glider. Find the length, l, of the card.
Find the mass, m₂, of the second glider.
Place the gliders on the track.
Blue tack is placed at the end of glider 2 and a point is placed at the end of glider 1.
This ensures that they will stick together after the collision.

Give glider 1 a gentle push.
Record the time, t₁, it takes to pass through the first light gate.
The gliders stick together.
Record the time, t₂, it takes the combination to pass through the second light gate.

Calculate the total momentum before, p₁, using the formula:
.

Calculate the total momentum after collision, p₂, using the formula:

Within the limits of experimental error, p₁ should be approximately equal to p₂.

SOURCES OF ERROR

• The track may not be horizontal.
• The error of parallax when measuring the length of the card.

SOLUTIONS

• Level the track using a spirit level.
• Ensure that your line of sight is at right angles to the ruler.