Standard 4.2
Motion, Forces, and Kinetic Energy

The student will investigate and understand characteristics and interaction of moving objects. Key concepts include
 ∑ motion is described by an objectís direction and speed;
∑ forces cause changes in motion;
∑  friction is a force that opposes motion; and
∑  moving objects have kinetic energy

Standard 4.2--
The Standard Curriculum Framework

The concepts developed in this standard include the following:
∑ The position of an object can be described by locating it relative to another object or the background.

∑ Tracing and measuring its position over time can describe an objectís motion.

Speed describes how fast an object is moving.

∑ A
force is any push or pull that causes an object to move, stop, or change speed or direction.

∑ The
greater the force, the greater the change in motion will be. The more massive an object, the less effect a given force will have on the object.

∑ Energy may exist in
two states: kinetic or potential.

∑ Kinetic energy is the energy of motion
.

Friction is the resistance to motion
created by two objects moving against each other. Friction creates heat.

Unless acted on by a force, objects in motion tend to stay in motion and objects at rest remain at rest. In order to meet this standard, it is expected that students should be able to:

∑ identify the forces that cause an objectís motion.
∑ describe the direction of an objectís motion: up, down, forward, backward.

∑ infer that objects have kinetic energy.

∑ design an investigation to determine the effect of friction on moving objects. 

Illustrated Content

A force is a push or a pull that causes an object to move, stop, or change speed or direction.  Every time you push or pull something you apply a force. Forces transfer energy.
When you throw a ball, the force of your arm pushes the ball into the air. Energy is transferred from your arm to the ball.
An object will stay in place until a force sets it in motion. 

The pull of gravity is a force that might set an object (or a skier) in motion. The pull or push of a magnet is another force that can move objects.  The force you exert with your legs or arms can set a ball in motion.

 

An object will continue to move until a force slows or stops it.  The force stopping the object's motion might be an obvious one - the ground!

Friction is a force that slows or stops motion.  Friction is the resistance to motion created by two objects rubbing against each other (the sled and the snow, for instance). Even air causes friction.  Friction creates heat.

The effect of a force depends on the object's mass.  More massive objects  have more "inertia".  This means a force will have less effect on a more massive object.  For example, it's easier to push a light plastic ball than a more massive boulder. It's also harder to stop a boulder when it is rolling down a slope. The more massive boulder has more "inertia".