MOTION IS EVERYWHERE. We walk to class. We drive to the store. A bird flies, the wind blows, rivers flow. The continents drift, and the Earth revolves on its axis. As you are beginning to figure out, motion involves movement. How do we decide if something is moving? A reference object must be used. Whenever you describe something that is moving, you are comparing it with something that is assumed to be stationary, or not moving ... that non-moving object is called a reference object. For example, if you were riding on a rollercoaster and looking outside, you could determine that you were moving by watching trees and buildings pass by. We know that a tree is a stationary object, so it would indicate movement. The most commonly used reference object is the Earth, but understand any stationary object would be a frame of reference. So in essence a change in location within a certain amount of time is motion.

Picture a race car at the starting line of the Talledega 500. Moments later the flag is waved and the cars take off. 500 miles later the cars approach the finish line. To more accurately describe motion, we use the word speed. Speed is the rate at which an object moves. Which car always wins race? The car that changes it location within the shortest amount of time. Think about this, how far did the cars travel? how long did it take them to cover the distance? Speed then is equal to distance divided by time! There are two types of speed - constant speed and average speed. Just like the term suggests, constant speed does not change. When you calculate the speed of an object at constant speed, you are figuring out its speed at every point along its path. The speed at which the Earth rotates is an example of constant speed. The speed of light traveling through the Universe is constant speed. On a graph, constant speed would be plotted in a straight line. The object would cover the same distance over the same amount of tijme. Sometimes the speed of an object must change. Imagine yourself driving through town on HWY 31. Your speed would not be constant because you will have to stop at several red lights.

Dividing the total distance traveled by the total time gives you average speed. If you were to plot average speed on a graph, the line would be crooked.

In addition to speed, another characteristic is needed to describe motion ... direction. Did the object move east, west, south, or north? To describe both the speed and the direction of motion, the term velocity is used. You may not think there is much difference between speed and velocity, but the direction given by velocity is very important. Think about an airport and planes taking off and landing. It is extremely important that air traffic controllers understand the concept of velocity, don't you think? You can combine the velocities of two different objects. Suppose you were rowing a boat down the river. You can combine the velocity of the boat along with the velocity of the moving river. This idea of combining velocities is very important, especially for launching rockets. Space engineers launch rockets in the same direction as the Earth rotates to get an added boost for escape velocity. When we are traveling in our cars we are constantly speeding up, slowing down and changing directions. This change in velocity is known as acceleration. Take a look at the animation below and decide which car is accelerating. Remember acceleration involves speeding up, slowing down, or changing direction.

The acceleration of an object is equal to its change in velocity divided by the time during which this change occurs. The change in velocity is the difference between the final velocity and the original velocity. Acceleration = fv - ov divided by the length of time the change took place.

What causes motion (what causes causes an object to change positions)? The answer is a force. A force is a push or pull on an object. A force gives energy to an object, sometimes causing it to start moving, stop moving, or change dirrection. To open a door you must push the door open, to close it you pull it shut. In both instances you are applying a force. What would happen if you increase the amount of force you exert? Think about two teams playing tug-of-war. If the two teams pull opposite of each other while exerting the same amount of effort, what happens to the red flag in the middle? That's right, it doesn't move. The forces that were applied were equal and opposite; and no motion occurred. This is an example of a balanced force. If forces are balanced, motion does not occur. What causes and object to move? An unbalanced force. Unbalanced forces occur when one force is greater than another force. Net movement is always in the direction of the greatest force. Think again about the tug-of-war and look at the diagram below!

Movement will always be toward the vehicle that exerts the greatest force.

Have you ever coasted on your bike along a level street? If so, you know that you continue to move for a while even though you have stopped pedaling. Every so often you pedal a little bit more and you coast further on. Early Greek philosophers made similar observations about objects in motion, to them for an object to move a force had to be applied. Later on, Issac Newton noticed that an object at rest had a tendency to stay at rest unless a force acted upon it. Newton called this phenomenon "inertia." Newton's 1st Law of Motion helps tie these two concepts together. In simple terms Newton stated that an object at rest will stay at rest and an object in motion will stay in motion unless a force acts upon them. In order for an ojbect's velocity (even if the object's velocity is zero) to be altered a force must be applied to that object. If a force is not applied, the object will maintain its velocity. If a person is riding a motorcycle that is going 50 mph North, what is that person's velocity? Your right, 50 mph North. Look at the animation below and ask yourself why is the rider ejected from the bike?

That's right, the rider is following Newton's 1st Law of Motion, he is maintaining his velocity.

Additional assignments- print and turn in your work, you'll need to install ShockWave:
1. Online Practice Test
2. Interactive Tutor

Upon completing this chapter students will be able to:
1. explain motion
2. describe how motion occurs with respect to a frame of reference
3. calculate speed
4. understand the importance of speed and velocity
5. define acceleration an deceleration