Collisions Lab

The BIG Question
   
    What is the difference between the amount of energy lost in an elastic collision vs. inelastic collision?
    What is a better conserved quantity- momentum or energy?

Background

• scalar quantities: magnitude (mass, energy, temperature)
• vector quantities: magnitude and direction ( + rightward, - leftward)
• types of collisions:
• elastic- objects bounce off each other
• inelastic: objects stick together
• momentum: p = m (v)
• mass (velocity)
• mass is measured in kilograms (kg)
• velocity is measured in meters per second (m/s)

• In this week's lab, our goal was to find the difference between the amount of energy lost in an elastic collision and inelastic collision. To test this, we put two cars of the same mass on opposite sides of a track, one red and one blue. We set two range finders on the ends of the track, which measure the velocity of the cars. These range finders were plugged into the electronic force probe, which was then plugged into the computer. The application on the computer graphed the velocity of both cars before, during, and after the collision.

• For the inelastic collision, we pushed the red car to the right toward the blue car, which then stuck together with velcro. Both cars continued to move together to the right. 

• For the elastic collision, we pushed the red car with a spring toward the blue car to the right. In this collision, the red car followed the blue car at a much slower pace once they hit, while the blue car continued to move to the right.

• We recorded our data and found the total momentum (p = mv) and the total kinetic energy (KE = 1/2mv^2) of both collisions.

• Then we found the percent difference of both the amount of energy and momentum that left or entered the system for both elastic and inelastic collisions.

• Percent difference: 

• Kinetic energy: (Total after - Total before)/(Total after + Total before / 2) (100)

• Momentum: (Total after - Total before)/(Total after + Total before / 2) (100) 

• We found that momentum is a better conserved quantity rather than energy because more energy is given off during a collision. Momentum has a smaller percent difference.

• We also found that inelastic collisions lose more energy than elastic collisions

Real Life Connection: 

      The game of pool uses the exact same concepts of momentum in collisions. When the white ball hits another colored ball, the hit and the colored ball keeps moving. The goal of the game is to get all the colored balls in the holes without knocking the white ball in with them. The velocity of the balls plays a key part in strategizing.