Motion 1

Motion & ForcesMotion & Forces

To describe Motion, we use these main terms:

Motion Speed / Velocity Acceleration

A. MotionA. Motion

Problem: Is your desk moving?

We need a reference point...A nonmoving point from which

motion is measured (you have to have one to measure motion!)

A. MotionA. Motion

MotionChange in position in relation to

a reference point.

Reference point

Motion

A. MotionA. Motion

Problem:You are a passenger in a car

stopped at a stop sign. Out of the corner of your eye, you notice a tree on the side of the road begin to move forward.

You have mistakenly set yourself as the reference point.

B. Speed & VelocityB. Speed & Velocity

Speed Is the rate of motion The distance traveled per unit

time

time

distancespeed

sd

t


Instantaneous Speedspeed at a given instant

Average Speed

time total

distance totalspeed avg.

we tend to use average speed… why?


Problem:A storm is 10 km away and is

moving at a speed of 60 km/h. Should you be worried?

It depends on the storm’s direction!


Velocity is essentially the same thing as

speed, but in a given direction

B. Resultant VelocityB. Resultant Velocity

combining 2 or more velocities together

if 2 velocities are in the same direction, add them together

if 2 velocities are in opposite directions, subtract the smaller velocity from the larger velocity, and use the direction of the larger velocity

B. Resultant VelocityB. Resultant Velocity

Think about a moving sidewalk… If you walk with the sidewalk, you walk faster than when you just ride the sidewalk, which is faster than if you were walking opposite to the moving sidewalk

C. CalculationsC. CalculationsYour neighbor skates at a speed of 4 m/s.

You can skate 100 m in 20 s. Who skates faster?

GIVEN:

d = 100 m

t = 20 s

s = ?

WORK:

s = d ÷ t

s = (100 m) ÷ (20 s)

s = 5 m/s

You skate faster!sd

t

C. CalculationsC. CalculationsSound travels 330 m/s. If a lightning bolt

strikes the ground 1 km away from you, how long will it take for you to hear it?

GIVEN:

s = 330 m/s

d = 1km = 1000m

t = ?

WORK:

t = d ÷ s

t = (1000 m) ÷ (330 m/s)

t = 3.03 s

sd

t

C. CalculationsC. CalculationsYou are traveling at an average speed of

60 miles per hour. In 1.3 hours, how far can you travel?

GIVEN:

s = 60 mph

t = 1.3 hours

d = ?

WORK:

d = s x t

d = (60 mph) x (1.3 hrs.)

d = 78 miles

sd

t

D. Graphing MotionD. Graphing Motion

slope =

steeper slope =

straight line =

flat line =

Distance-Time Graph

A

B

faster speed

constant speed

no motion

speed


Who started out faster? A (steeper slope)

Who had a constant speed? A

Describe B from 10-20 min. B stopped moving

Find their average speeds. A = (2400m) ÷ (30min)

A = 80 m/min B = (1200m) ÷ (30min)

B = 40 m/min

Distance-Time Graph

A

B


0

1

2

3

0 2 4 6 8 10

Time (s)

Sp

ee

d (

m/s

)

Speed-Time GraphLine going down =

slowing downLine going up =

speeding up

Flat (horizontal) line = moving at a constant speed

Speed of zero = not moving


0

1

2

3

0 2 4 6 8 10

Time (s)

Sp

ee

d (

m/s

)

Speed-Time GraphSpecify the time period

when the object was... slowing down

5 to 10 seconds speeding up

0 to 3 seconds

moving at a constant speed 3 to 5 seconds

not moving 0 & 10 seconds

Education

Motion 1