Conceptual Physics--Chapter 3: Linear Motion

Linear motion

Motion along a straight-line path.

Constant velocity

Motion in a straight line at a constant speed.

Free Fall

Motion under the influence of gravity only.

If a projectile is fired straight up at a speed of 10 m/s, the time it takes to reach the top of its path is about

1 second

Distance fallen in free fall, from rest;

*d = ½ gt²*

Velocity acquired in free fall, from rest;

*v = gt*

A horse gallops a distance of 10 kilometers in a time of 30 minutes. Its average speed is

20 km/h

At one instant a heavy object in air is moving upward at 50 meters per second. One second later its speed is approximately

40 m/s

Speed =

Distance ------------ Time

Speed

How fast something moves; the distance traveled per unit of time.

Changing velocity

If either the speed or the direction changes (or both change), then the velocity changes.

Vector quantity

Quantity in physics that has both magnitude and direction.

Instantaneous speed

Speed at any instant.

Constant speed

Steady speed.

Acceleration

The rate at which velocity changes with time; the change in velocity may be in magnitude, or direction, or both.

Velocity

The speed of an object and a specification of its direction of motion.

acceleration is not velocity, nor is it even a change in velocity... it is

acceleration is the rate at which velocity itself changes

Acceleration (along a straight line) =

change in speed --------------------- time interval

Acceleration =

change of velocity ----------------------- time interval

The two measurements necessary for calculating average speed are

distance and time

In each second of fall, the distance a freely falling object will fall is

increasing

Motion

is relative.

Twelve seconds after starting from rest, an object falling freely will have a speed of

more than 100 m/s

Drop a rock from a 5-m height and it accelerates at 10 m/s2 and strikes the ground 1 s later. Drop the same rock from a height of 2.5 m and its acceleration of fall is about

the same

Average speed =

total distance covered ---------------------------- time interval

A car maintains a constant velocity of 100 km/hr for 10 seconds. During this interval its acceleration is

zero