Chapter 4

Relative- The motion of one object with respect to anoter

• Relative- The motion of one object with respect to another.
• An object is moving if its position relative to a fixed point is changing.

4.2 Speed

• Speed- how fast an object is moving
• You can calculate the speed of an object by diving the distance covered by time
• instantaneous speed- The speed at any distence
• Average speed- Total distance covered divided by time

4.3 -Velocity- speed in a given direction -Speed is a description of how fast an object moves; velocity is how fast and in what direction it moves

• Velocity- Speed in a given direction
• Speed is a description of how fast an object moves; velocity is how fast and in what direction it moves

4.4 Acceleration

• Acceleration-- The rate at which the velocity is changing
• You can calculate the acceleration of an object by dividing the change in its velocity by time

4.5 Free Fall: how fast

• Free fall- An object moving under the influence of the gravitational force only
• Elapsed Time- The time that has passed since the beginning of motion, in this case the fall
• The acceleration of an object in free fall is about 10 meters per second squared.

4.7 GRAPHS of MOTION

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

Untitled Slide

4.8 Air resistance and falling objects

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

4.9 How fast, how far, how quickly, how fast changes

• Acceleration is the rate at which velocity itself changes
• Vector- quantity with magnitude and direction.
• V=d/t and s=d/t and a=acceleration*v over time

1. How can you be both at rest and also moving about 107,000 km/h at the same time?
Because the world is moving and that means everything is moving all the time.

2. You cover 10 meters in a time of 1 second. Is your speed the same if you cover 20 meters in 2 seconds ?
Yes

Does the speedometer of a car read instantaneous speed or average speed?
Instantaneous.

Average speed=distance covered divided by travel time. Do some algebra and multiply both sides of this relation by travel time. What does the result say about distance covered? That the more you run the more you gain distance.

Which is a vector quantity, speed or velocity?
Speed

What two controls on a car cause a change in speed? What control causes only a change in velocity?
The brake and gas pedal. The steering wheel.

What is the acceleration of a car moving along a straight-line path that increases its speed from zero to 100 km/h in 10s?
The acceleration is 10 km/h

By how much does the speed of a vehicle moving in a straight line change each second when it is accelerating at 2 km/h? At 4 km/hs? At 10km/hs?
2 km/h, 4 km/h, and
10 km/h

Why does the unit of time enter twice in the unit of acceleration?
Because acceleration is measured by velocity.

What is the meaning of free fall?
An object moving under the influence of the gravitational force only.

For a free falling object dropped from rest, what is the instantaneous speed at the end of the fifth second of fall? The sixth second?
50 km/h and 60 km/h.

How far will a freely falling object fall from rest in 5 seconds? Six seconds?
Its depends on the object that is falling.

How far will an object move in one second if its average speed is 5 m/s?
It will move 5 meters.

how far will a freely falling object have fallen from a posistion of rest when its instantaneous speed is10 m/s?
25 meters.

what does the slope of the curve on a distance-versus-time graph represent?
It represents the points that form a straight line.

What does the slope of the curve on a velocity-versus-time graph represent?
It is the vertical change divided by the horizontal change for any part of the line.

what is the appropriate equation for how fast an object freely falls from a position of rest? For how far that object goes?
1.v=gt.
2. d=1/2gt squared.

Does air resistance increase or decrease the acceleration of a falling object?
It decreases.

what is the appropriate equation for how fast an object freely falls from a position of rest? For how far that object goes?
1.v=gt.
2. d=1/2gt squared.