# Velocity

In this experiment you can actually see velocity at work.  Velocity is speed plus direction.  A car traveling in a straight line at a constant speed has a constant velocity, but if the car turns around a curve in the road then the velocity changes, even if the speed stays the same.  Or a car that is changing in speed, even if it continues in the same direction, has a changing velocity.  A car with both a changing speed and changing direction also has a change in velocity.  A change in velocity is an acceleration, even if only the direction changes and not the speed.

## Velocity Experiment

This is an apparatus that will allow you to see changes in velocity.

You need a:

• 2 liter bottle
• cork
• push pin
• string
• water
1. Fill the bottle with water.
2. Attach a string to the cork with a push pin then tie the other end of the string to the mouth of the bottle.  Drop the cork into the water.
3. Put the cap on tightly.
4. Turn the bottle upside down on a table or counter top.
5. Move the bottle along the surface at a constant speed and direction.  Observe the cork.
6. Then experiment with moving the bottle in different ways, changing direction suddenly, speeding up quickly, coming to a sudden stop.  Observe the cork again.

Isaac is moving the bottle along at a constant speed and direction. The cork floats straight up in the center of the bottle.

Isaac suddenly changes direction and the cork moves to one side of the bottle.

If the cork stays floating in the center of the bottle then there is no change in velocity (or at least not enough for the cork to register).  If the cork moves to the side of the bottle then you are registering a change in velocity, an acceleration.