Rocking Critter

   Ironically, this simple playground feature is, to us, one of the most difficult to understand when talking about physics.

    In this section there are several key words that we MUST know in order to understand the physics behind the Rocking Critter.

Force- a force is a push or a pull, measured in Newton’s. A force is equal to mass times acceleration. In the Rocking critter, one accelerates ones’ self in order to exert a force on the spring.

Spring Constant- this is a quantitative measure of the stiffness of the spring

Compression and expansion- In areas of compression the spring comes close together. In areas of expansion the spring spreads apart.

Velocity- velocity is equal to displacement / time. This is the measure of the speed and direction of a said object. In talking about the rocking critter it tells us how fast the spring expands and contracts.

Period- The period is the amount of time it takes for the spring to make one complete oscillation or cycle.

Mass- The mass of a person is directly related to how much force they can exert on the spring. It is also used in determining velocity.

    The Rocking Critter is usually a large spring with some type of animal shaped seat on top. The basic principle is that all actions have and equal and opposite reaction. As you exert a force in one direction, the spring offers resistance and restoring force that oppose your force. The spring pushes you back in an attempt to stay vertical. This can result in a "wacky ride", the rider thrusts about wildly and is pushed back by the critter. This is usually a ride liked by youngsters.

The properties of the spring are determined by the spring constant (k). This determines the extent of the restoring force. The restoring force is the equal and opposite reaction, in areas of compression the restoring force pushes, in expansion the restoring force is a pull.

The restoring force is equal to the spring constant times the amount of stretch or compress in meters (f= -kx). The force needed to distort the spring is equal to the KE or force exerted.

It is also possible to determine the velocity and period of the spring.

sqrt=square root

V=Sqrt[(x_o² - x_f²)k/m] where x_o= X original and x_f= X final. This formula uses the spring constant to determine how the spring will react to a certain mass.

The formula for period is T= 2p sqrt(m/k) sqrt=square root. And like the swing the frequency is the inverse of the period.

This picture demonstrates these principles: