# Unit 7!

## 27 terms

### motion

an object's change in positon relative to a reference point.

### reference frame

a group of objects that do not move relative to each other.

### displacement

the change in postion of an object.

### speed

the distance traveled by an object divided by the time interval during which the motion occured.

### average speed

a rate of motion determined by dividing the total distance traveled by the total travel time.

### velocity

the speed of an object in a particular direction.

### resultant velocity

the sum of all the velocities of an object combined.

### acceleration

the rate at which velocity chanes over time; an object accelerates if its speed, direction, or both change.

### deceleration

decrease in velocity.

### centripetal acceleration

the acceleration directed toward the center of a circular path.

### distance-time graph

graph in which distance is measured against time.

### velocity-time graph

A graph that can be used to plot the velocity of an object versus time and to determine the sign of an object's acceleration.

### constant acceleration

is a steady change in velocity.

### force

the combination of all the forces acting on an object.

### net force

a single force whose external effects on a rigid body are the same as the effects of several actual forces acting on the body.

### balanced force

equal forces acting on one object in opposite directions.

### unbalanced force

two or more forces that are not equal and opposite of one another; can cause change in motion.

### friction

a force that opposes motion between two surfaces that are in contact.

### static friction

the foce that resists the intention of sliding motion between two surfaces that are in contact and at rest.

### kinetic friction

the foce that opposes the movement of two surfaces that are in contact and are sliding over each other.

### sliding friction

friction that occurs when one solid surface slides over another.

### rolling friction

friction that occurs when an object rolls over a surface.

### fluid friction

friction that occurs as an object moves through a fluid.

### streamlining

the science of shaping objects so they allow the easy flow of fluids around them to reduce drag.

### lubricants

substances that are applied to surfaces to reduce friction between them.

### harmful friction

unwanted friction causing damage. ex: fire, carpet burn.