My PBL Project

Introduction

My project is called "Newton's Cradle". The main purpose of my project is to illustrate how the Law of Inertia, the conservation of momentum, and Newton's Third Law is used within the Newton's Cradle.

Materials

• Newton's Cradle

• Balls of various weights to be used in the cradle

Procedures

1. Start by pulling back one ball.

2. Release the ball.

3. Watch as the energy and the momentum transfer from the first ball to the last ball.

4. Observe the cycle you have created.

5. Tweak the experiment by pulling back two balls.

Safety

There are not any safety concerns for this experiment.

Pictures and Video

Scientific Principle

The Newton's Cradle demonstrates the principle of the conservation of momentum. This principle states that when the two objects collide, the total momentum of the objects before the collision is equal to the total momentum of the objects after the collision. In other words, when the first ball of Newton's Cradle collides with the second, the first ball stops, but its momentum isn't lost, just transferred to the second ball, then the third, then the fourth, until it reaches the very last ball. You witness this conservation of momentum as the last ball swings into the air with nearly the same momentum as the first ball. The same happens when two balls are lifted. If two balls are lifted into the air on one end of the cradle and released, then two balls on the opposite end will swing in response. This continuous clicking of balls is also proof of Newton's Law of the conservation of energy, which states that energy can't be created or destroyed but that it can change forms. Newton's Cradle demonstrates this last part of the law quite well, as it converts the potential energy of one ball into kinetic energy that is transferred down the line of balls and ultimately results in the upward swinging of the last ball.

Real Life Application

The game of pool provides an example of a collision in which one object, the cue ball, is moving, while the other—known as the object ball—is stationary. Due to the hardness of pool balls, and their tendency not to stick to one another, this is also an example of an almost perfectly elastic collision—one in which kinetic energy is conserved.

Investigation Questions

1. How does the Newton Cradle demonstrate Newton Third Law of Motion?

The force of the first ball causes and equal and opposite reaction in the ball at the other end.

2. When one ball collided with the other four balls how many of the balls moved in response to the collision? Why?

One ball moved in response to the collision because the energy and momentum was transferred to the ball the moved.

3. Is the Newton's cradle elastic or inelastic collision?

Inelastic collisions, in which the kinetic energy after the collision is less than the kinetic energy beforehand. This happens because the balls themselves are not perfectly elastic because they can't escape the effect of friction.

4. What exactly is the Newton's Cradle?

Newton's cradle, named after Sir Isaac Newton, is a device that demonstrates conservation of momentum and energy with a series of swinging spheres.