Chapter 2Linear Motion

- Motion of some form is responsible for nearly

everything we see, do, or experience in our daily

lives. - Quantity divided by time is RATE

Motion is Relative - 2.1

- When we see things move in the world around us,

they are moving relative to us and our position. - It is important to realize that in relative to

the sun and stars everything on the earth is

moving. - In this class, when we talk about motion we will

be looking at it relative to the surface of the

earth.

SPEED 2.2

- SPEED is the measure of how fast something is

moving, or the rate at which a distance is

covered. - Speed distance / time
- The units for speed can be any measure of

distance over any measure of time. It is written

as Dist./Time - The speed of any object at any given instant is

its instantaneous speed.

Speed (cont.)

- The speed of any object over a period of time is

its average speed. - When distinguishing between instantaneous and

average speed think of a road trip. - The equation for average speed is total distance

divided by total time interval. - Speed Dist. / Time

Velocity 2.3

- There is a difference between speed and

velocity Speed is how fast you are

traveling Velocity is how fast you are traveling

and what direction you are going. This means

that your speed can be constant while your

velocity is changing if you are going around a

turn.

Velocity (cont.)

- Constant velocity means constant speed and

constant direction - Changing velocity can mean either speed or

direction are changing or both!

Acceleration 2.4

- When velocity is changing then we have

acceleration. Acceleration change in

velocity / time interval - Acceleration applies to both a increases and

decreases in speed (often times we use the term

deceleration when we talk about slowing down, but

in physics we use acceleration for both) - Acceleration also applies to change in direction.
- The units used is distance / time / time
- or distance / time2

Free Fall 2.5 How Fast

- When an object is dropped it falls, and as it

falls its speed increases. If we neglect air

resistance, we say it is free falling if no other

forces are acting on it except gravity. The

amount of time that has passed since the

beginning of the fall is the elapsed time.

Free Fall (cont.)

- To get the instantaneous speed of an object in

free fall that is dropped from rest we say

velocity equals acceleration times time, where

acceleration is due to gravity. - v gt V is velocity, g is acceleration

due to gravity, and t is elapsed time - This equation can be written as v at a is

acceleration an object undergoes

Free Fall (cont.)

- The acceleration due to gravity is equal to 9.8

m/s/s, which we commonly round to 10

m/s/s. This means for each second an object

falls, its instantaneous speed increases 10

m/s.

Free Fall (cont.)

- All rules for an object in free fall that is

falling downward also apply to an object in free

fall upwards, except in this case, the

acceleration due to gravity is negative and the

speed is decreases each second by 10 m/s.

Free Fall 2.6 How Far

- When looking at how far an object falls in free

fall it is important to remember the difference

between instantaneous and average speed. Remember

that average speed is how far an object has

traveled divided by the amount of time it has

been traveling. This means that after one

second an object in free fall is falling 10 m/s.

It started at 0 m/s. The average of 10 and 0 is

5, so the average speed for one second is 5 m/s.

Free Fall (cont.)

- Put this into the equation Average Velocity

distance traveled / time period - we get a distance of 5 m
- This could get complicated if we start looking at

longer time periods, because each second the

speed is changing. To deal with this we use the

following equation.

Free Fall (cont.)

- d vot ½ gt2 d is distance, g is

acceleration due to gravity, and t is the elapsed

time - The equation can also be written as d vot 1/2

at2

Graphs of Motion 2.7

- Some times it is easier to look at a graph to see

the relationships between distance, velocity, and

acceleration. Here are some guidelines for

looking at motion graphs - Distance VS Time graphs
- 1. a flat straight line indicates there is no

acceleration. - 2. A diagonal line indicates constant velocity
- 3. A curved line or a line that stops and starts

indicates there is some acceleration happening

Graphs of Motion

- Velocity VS Time graphs
- A flat line indicates there is motion, but it is

happening at a constant rate and there is no

acceleration. - A diagonal line indicates a constant acceleration
- A line that is not straight indicates an

acceleration that is not constant.

Air Resistance 2.8

- Air resistance changes the motion of all moving

objects.

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