Motion

Ch. 1

Motion- a change in position

Frame of Reference

Frame of Reference (reference point)- Whenever you describe something that is moving you compare it to something that is usually stationary

This background or object that is used for comparison is called the frame of reference

Earth is the most common frame of reference.

Are you in motion?

If you and your friend are walking down the hall together at the same speed, in the same direction.

- Is she moving relative to you?

-Are you moving relative to her?-Are either of you moving

relative to the earth?

Distance

The length of the

route you travel.

start

finish

Displacement

The direction and

difference in the position

between your starting

and ending points start

2.7 km to the South

END

Speed- the rate at which an object moves

Speed = Distance ÷ Time

Example: A car travels 300km in 6 hours. What is the speed of the car?

3 Steps to Solve Speed Problems

Step 1: Write the Formula

Step 2: Plug in the numbers (including the units)

Step 3: Solve (including the units)

A car travels 300km in 6 hours. What is the speed of the car?

(Speed = distance ÷ time) Step 1: S = D/TStep 2: S = 300km ÷ 6 hoursStep 3: S = 50km/hr

Velocity

Velocity- speed in a given direction

Merry go round-always changing velocity why?

Ex: A runner moves eastward at 10 m/s.

What is the speed?

What is the velocity?

Why is velocity important?

Constant Speed

Constant Speed-(rare) speed which is the same throughout the movement, does not change throughout the journeyWhen you calculate the speed of an object traveling at constant speed, you are figuring out it’s speed at every point in it’s path-(at every point the speed is the same)Graph-straight diagonal line

Average Speed

Average Speed-usually speed changes many times through a journey…speed equals distance divided by time

S= D T

Speed varies so you find average speed

On a distance vs. time graph…

*1. Distance is on the y-axis and time is on the x-axis.

Distance (m)

Time (sec)

distance-time graphs….

2. The steeper the line means the faster the object/person is moving.

3. A straight diagonal line means speed is constant.

4. A straight horizontal line means the object or person is not

moving (at rest).

5. At any given point the speed can be calculated

At point A in the Speed graph, it represents the object/ person on its way back to the original starting point. Notice the y-axis is labeled position, it is the same as distance.

A

Distance v. Time

Acceleration

Acceleration- rate of change in velocity

A= Sf-Si

T

Acceleration

3 Types:

Speeding Up

Slowing Down

Changing Position

Acceleration

Acceleration measured in meters per second per second or m/s/s or m/s2

For example, during the running lab if a student had an

acceleration of 5 m/s/s then for every second that went by his speed

increased 5 m/s

When an object slows down, it is decelerating or negative acceleration-still accelerating but decreasing

On a speed vs. time graph (graph that shows acceleration of an object):

• 1. Speed is labeled on the vertical y axis.

• 2. Time is labeled on the horizontal x axis.

Acceleration graph

3. A straight horizontal line on the graph represents constant speed (no

acceleration).

4. When the diagonal line rises (slopes upward), the object is speeding up (positive

acceleration).

5. When the diagonal line is falling (slopes downward), the object is slowing

down (negative acceleration or deceleration).