Resource: Carnival Physics: Midway Games

Two common carnival games, "Break the Plate" and "Knock the Blocks off the Table," require energy (the ability to do work or make changes to the physical world) to win. Where does that energy come from? The energy comes from you, the player.

When you throw a ball, you transfer energy to the ball. The amount of kinetic energy, or energy of motion, that the ball has is related to both its mass and its speed. For example, a ball thrown at a given speed has more kinetic energy then a less massive ball thrown at the same speed. In addition, a ball thrown at a given speed has more kinetic energy than a ball of the same mass thrown at a slower speed. You are more likely to win if the ball has a lot of energy to break the plate or move the blocks.

When the ball strikes an object, such as a plate or a block, the impact transfers energy from the ball to the object, exerting a force on the object. In general, a force (such as a push or a pull) changes the motion of an object. The size of the change is related to the strength of the force—a greater force results in a bigger change. In these carnival games, you need to strike the blocks with enough force to knock them down or hit the plate with enough force to break it.

Interestingly, it turns out that the position of the plate plays a big part in determining the amount of force that will act on it. This can be explained in terms of momentum—a quantity that describes how much motion an object has. All moving objects possess momentum. In a collision, the force created by the impact is related to the rate of change of momentum; extending the duration of the impact decreases the amount of force.

For example, safety airbags in cars extend the duration of the impact between a person and the windshield. Instead of hitting the windshield with a sharp impact that would produce a lot of force (which could injure a person and damage the windshield), the airbag makes the collision occur over a longer period of time, which minimizes the forces acting on the objects involved. In the game, when the plate is leaning forward, the time of impact is extended (as the ball makes contact and moves the plate backward), reducing the force acting on the plate and making the plate less likely to break.

To learn more about energy, check out Potential and Kinetic Energy: Spool Racer, Energy in a Roller Coaster Ride, and Energy Transfer in a Trebuchet.

To learn more about momentum, check out Momentum and Collisions on an Air Track.

To learn more about the motion of projected objects, check out Projectile Motion.

To learn more about how air bags work, check out Air Bag Design.

• How would you describe the interaction between the ball and the blocks?
• Discuss the effect of the plate's angle on the girls' success in smashing it. How would you explain it in terms of force? Energy? Momentum?
• Why do you suppose the softball was more effective at scattering the blocks and the dimpled ball at breaking the plates?