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What do we mean when we say that mortion is relative? what is everyday motion usually relative to?

motion is the movement of one thing compared to another. We usually use earths surface as the refrence.

speed is the rate at which what happens?

the rate at which distance changes with time.

you walk across the room at 2 kilometers per hour. Express this speed using abbreviated units.

2km/h

what is the difference between instantaneous speed and average speed?

instantaneous speed is the speed at any given instant,whereas average speed is the quotient(division) of total distance and total time.

does the speedometer of a car read instantaneous speed or average speed?

it displays instantaneous speed.

what is the difference between speed and velocity?

velocity is a vector quantity;it describes both speed and direction.

if the speedometer of a car reads a constant speed of 40km/h can you say that the car has a constant velocity?

No. If the car is changing direction, the velocity is changing even though the speed remains constant.

What two controls on a car cause a change in speed? what control causes only a change in velocity?

accelerator and brake. steering wheel

what quantity describes a change in velocity?

acceleration

Acceleration is the rate at which what happens?

The rate at which velocity changes.

What is the acceleration of a car that travels in a straight line at a constant speed of 100 km/h?

0, as neither speed nor direction are changing.

What is the acceleration of a car moving along a straight-line path that increases it's speed from 0 to 100km/h in 10 seconds.?

ten km/hxs

by how much does the speed of a vehicle moving in a straight line change each second when it is accelerating at 2 km/hxs? 4 km/hxs? 10 km/hxs?

2 km/h, 4 km/h, 10 km/h

why does the unit of time enter twice in the unit of acceleration?

because it is a change over time in speed, and speed already has a time unit in it(distance/time).