# Linear Motion

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Vocabulary words and important facts from Chapter 4: Linear Motion from the Prentice Hall Conceptual Physics textbook. Big Idea: You can describe the motion of an object by its position, speed, direction, and acceleration.

### How can you tell if an object is moving?

An object is moving if its position relative to a fixed point is changing.

### speed

how fast an object is moving

### instantaneous speed

the speed of an object at any instant

### average speed

the total distance covered divided by the time

### How can you calculate speed?

You can calculate the speed of an object by dividing the distance covered by the time.

### velocity

speed in any given direction

### How is velocity different from speed?

Speed is a description of how fast an object moves; velocity is how fast and in what direction it moves.

### acceleration

the rate at which the velocity is changing

### How do you calculate acceleration?

You can calculate the acceleration of an object by dividing the change in its velocity by time.

### free fall

when an object is moving only by influence of gravitational force

### elapsed time

the time that's passed since the beginning of any motion

### What is the acceleration of an object in free fall?

The acceleration of an object in free fall is about ten meters per second squared.

### For a falling object, how does the distance per second change?

For each second of free fall, an object falls a greater distance than it did in the previous second.

### What does a slope of a speed-versus-time graph represent?

On a speed-versus-time graph the slope represents speed per time, or acceleration.

### How does air resistance affect falling objects?

Air resistance noticeably slows the motion of things with large surface areas like feathers or pieces of paper. But air resistance less noticeably affects the motion of more compact objects like stones or baseballs.

### What is the relationship between velocity and acceleration?

Acceleration is the rate at which velocity itself changes.

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