Part 1: Describing Motion

The Earth has a steady, or constant, motion as it moves around the sun.

Vehicles have variable motion. They move in many directions and at many different speeds.

A pendulum has periodic motion. It swings back and forth.

Wheels move in a circular motion.

A rubber band vibrates when you pluck it.

Speed and Velocity

Average speed describes how far an object moves during a certain amount of time.

To calculate average speed, use this formula:  Average Speed = Distance Time

That means if a car moved 100 meters in 20 seconds, its average speed would be: 100 m = 5 m 20 s s 5 meters per second

We are always moving. Even when we appear to be still, we are moving. Right now we are all moving around the sun faster than a rocket.

So, you can’t always tell that an object is moving just by looking at it.

Motion is always measured in relationship with some location called a point of reference.

For example, if I’m on board a cruise ship, I can walk to the end of the moving ship. Let’s say I walk 300 meters to the end of the ship and it takes me 150 seconds. Average Speed = meters seconds Average Speed = 300 m = 2 meters per second 150 s

Within the ship I am moving 2 meters per second. However, if I use another point of reference, like a lighthouse, I’m moving as fast as the ship.

Let’s say the ship is moving 300 meters in 10 seconds. Using the light house as the point of reference, I’m moving at 30 meters per second. Average Speed = 300 m = 30 meters per second 10 s

Velocity is different from speed.

Velocity describes the speed and the direction of an object’s motion.

The ship may be moving at a speed of 30 meters per second, but its velocity is 30 meters per second south east.

A skydiver might have the velocity of about 200 kilometers per hour down.