What do we mean when we say that motion is relative? What is everyday motion usually relative to?
It is measured in a reference frame; usually Earth's surface.
Speed is the rate at which what happens?
Distance changes with time.
You walk across the room at 2 kilometers per hour. Express this speed using abbreviated units.
2 km/h.
What is the difference between instantaneous speed and average speed?
Speed at an instant vs. total distance divided by time.
Does the speedometer of a car read instantaneous speed or average speed?
Instantaneous Speed.
What is the difference between speed and velocity?
Veocity describes both speed and direction.
If the speedometer of a car reads a constant speed of 40 km/h, can you say that the car has a constant velocity? Why or why not?
No, it may be changing direction at constant speed.
What two controls on a car cause a change in speed? What control causes only a change in velocity?
Accelerator and brake pedal; steering wheel.
What quantity describes how quickly you change how fast you're traveling, or how quickly you change your direction?
Acceleration.
Acceleration is the rate at which what happens?
Velocity changes.
What is the acceleration of a car that travels in a straight line at a constant speed of 100 km/h?
Zero; there is on change in velocity.
What is the acceleration of a car moving along a straight-line path that increases its speed from zero to 100 km/h in 10 s?
10 km/hs.
By how much does the speed of a vehicle moving in a straight line change each second when it is accelerating at 2 km/hs? At 4 km/hs? At 10 km/hs?
2 km/h; 4 km/h; 10 km/h.
Why does the unit of time enter twice in the unit of acceleration?
Once for speed change, again for time change.
What is the meaning of free fall?
Fall is free of air draf and forces other than gravity.
For a freely falling object dropped from rest, what is the instantaneous speed at the end of the fifth second of fall? The sixth second?
50 m/s; 60 m/s (when g= 10 m/ss).
For a freely falling object dropped from rest, what is the acceleration at the end of the fifth second of fall? The sixth second? At the end of any elapsed time t?
9.8 m/ss (or approximately 10 m/ss) at all times.
Toss a ball upward. What is the change in speed each second on the way up? On the way down?
9.8 m/s (or approximately 10 m/s) at all times.
How far will a freely falling object fall from rest in five seconds? Six seconds?
125 m ; 180 m.
How far will an object move in one second if its average speed is 5m/s?
5 m.
How far will a freely falling object have fallen from a position of rest when its instantaneous speed is 10m/s/
5 m (its average speeed would be 5 m/s).
What does the slope of the curve on a distance-versus-time graph represent?
Speed.
What does the slope of the curve on a velocity-versus- time graph represent?
Acceleration.
Does air resistance increase or decrease the acceleration of a falling object?
Decrease.
What is the appropriate equation for how fast an object freely falls from a position of rest? For how far that object falls?
V= gt; d= 1/2 gtt.