Chapter 3 Flashcards
Speed
How fast an object moves; the distance traveled per unit of time.
Instantaneous speed
The speed at any instant.
Average speed
The total distance traveled divided by the time of travel.
Velocity
An object’s speed and direction of motion.
Vector quantity
A quantity that has both magnitude and direction.
Scalar quantity
A quantity that has only a magnitude, not a direction.
Acceleration
The rate at which velocity changes with time; the change in velocity may be in magnitude, or direction, or both.
Free fall
Motion under the influence of gravity only.
As you read this in your chair, how fast are you moving relative to the chair? Relative to the Sun?
You are not moving relative to the chair, but you are moving 107,000 km/h relative to the Sun.
What two units of measurement are necessary for describing speed?
Distance and time.
What kind of speed is registered by an automobile speedometer: average speed or instantaneous speed?
Instantaneous speed.
What is the average speed in kilometers per hour of a horse that gallops a distance of 15 km in a time of 30 min?
30 km/hr.
How far does a horse travel if it gallops at an average speed of 25 km/h for 30 min?
12.5 km.
What is the main difference between speed and velocity?
Velocity includes a direction, but speed does not.
If a car moves with a constant velocity, does it also move with a constant speed?
Yes, because constant velocity requires constant speed in the same direction.
If a car is moving at 90 km/h and it rounds a corner, also at 90 km/h, does it maintain a constant speed? A constant velocity?
It maintains a constant speed, but does not maintain a constant velocity.
What is the acceleration of a car moving along a straight road that increases its speed from 0 to 100 km/h in 10 s?
10 km/h·s.
What is the acceleration of a car that maintains a constant velocity of 100 km/h for 10 s? (Why do some of your classmates who correctly answer the preceding question get this question wrong?)
0 km/h·s (Since the car’s change in velocity is zero).
When are you most aware of your motion in a moving vehicle: when it is moving steadily in a straight line or when it is accelerating? If you were in a car that moved with absolutely constant velocity (no bumps at all), would you be aware of motion?
Accelerating. You would not be aware of the motion if you did not look outside the car.
Acceleration is generally defined as the time rate of change of velocity. When can it be defined as the time rate of change of speed?
When moving in a straight line, the time rate of change of speed is acceleration.
What did Galileo discover about the amount of speed a ball gained each second when rolling down an inclined plane? What did this say about the ball’s acceleration?
The ball had constant acceleration, so it gained the same speed every second.
What relationship did Galileo discover about a ball’s acceleration and the steepness of an incline? What acceleration occurs when the plane is vertical?
The steeper the incline, the greater the acceleration. On a vertical incline, the ball is in free fall.
What exactly is meant by a “freely falling” object?
An object in free fall falls under gravity alone with no friction.
What is the gain in speed per second for a freely falling object?
It gains approximately 10 m/s.
