MotionChapter 2

What is motion?

?

Describing Motion Motion occurs when

an object changes position relative to a reference point.

A reference point is a a point of comparision

Earth is the most common reference point

Speed The distance an object

travels in a set amount of time

Speed = Distance = D = D

Time T T

How to use the Speed formula:

SPEED= DistanceTime

TIME= DistanceSpeed

DISTANCE= Speed x Time

Solving for Speed Solving for Time

Solving for Distance

What is the easiest way to remember these formulas without memorization? S

D

T

Let’s Practice

A windsurfer travelled 28 km in 1 hour 45 minutes. Calculate his speed.

How do we change time into a decimal?

Let’s approach time like we do money. How many quarters are in 1 dollar? How many 15 minutes are in 60 minutes?

15 minutes is ______ of 60 minutes

15 minutes = ___ = _____

30 minutes = ___ = _____

45 minutes = ___ = _____

¼ 0.25

½ 0.50

¾ 0.75

How do we change time into a decimal?

But what if it’s a random time? Take the time given and divide by 60

22 minutes = _______ = _____

47 minutes = _______ = _____

52 minutes = _______ = _____

98 minutes = _______ = _____

22/60 0.367

47/60 0.783

52/60 0.867

98/60 1.63

How do we convert time to a different unit?

What if you are given mi/hr and min? How would you do this problem?

You will have to convert one time unit so they both match! NEVER CONVERT THE UNIT

ALREADY ATTACHED TO SOMETHING!

CONVERT THE UNIT BY ITSELF!

How do we convert time to a different unit?

Going Large to Small:Multiply number by how many (you want) are in

(what you have)For example:

3 hours into minutes3 x 60 (60 min in 1 hour) = 180 mins

56 days into hours56 x 24 (24 hrs in 1 day) = 1344 hrs

24 hours into seconds24 x 60 (60 mins in 1 hr) = 1440 mins1440 x 60 (60 sec in 1 min) = 86400 sec

How do we convert time to a different unit?

Going Small to Large: Divide number by how many (you have) are in

(what you want) For example:

22 seconds into minutes 22 / 60 (60 seconds in 1 minute) = 0.367

min 375 hours into days

375 / 24 (24 hours in 1 day) = 15.625 days 3852 seconds into hours

3852 / 60 (60 sec in 1 min) = 64.2 min 64.2 / 60 (60 min in 1 hr) = 1.07 hour

Let’s Practice

A windsurfer travelled Northwest 28 km in 1 hour 45 minutes. Calculate his speed.

Speed = Distance

Time

Speed = _______

Speed =

Let’s Practice

A salesman travelled at an average speed of 50 km/hr towards Ohio for 2 hours and 8 mins. How far did he travel?

Distance =

Speed x Time

Distance =

Distance =

Let’s Practice

A train travelled from Nashville to Chicago, 470 miles, at an average of 60 mph. How long did the journey take?

Time = Distance

Speed

Time = ______

Time =

Speed The distance an object

travels in a set amount of time

Speed = Distance = D = D

Time T T

Velocity The distance an object travels

in a set amount of time in a SPECIFIC DIRECTION

Velocity = Speed + Direction

Velocity = Distance+Direction

Time

So basically… speed and velocity ARE THE SAME

THING! For velocity, you must just include the

direction of motion!!!

Speed = 60 mph Velocity = 60 mph

to the left

Acceleration Acceleration is the rate

of change of velocity Remember, velocity

includes both speed and direction, so acceleration also includes speed and direction.

So a change in velocity can either be: A change in how fast A change in direction

Acceleration occurs when an object

changes its speed, direction, or both.

Acceleration Positive

Acceleration is when an object speeds up. It is a positive #

Negative acceleration is when an object slows down. It is a negative # Also known as

deceleration

How to calculate Acceleration:

ACCELERATION = velocity = change in velocitytime time

a = vf – vi

t

Change in velocity = final velocity – initial velocity

ACCELERATION = final velocity – initial velocitytime

Calculating + Acceleration:

a = vf – vi

t

A jet airliner starts at rest at the end of a runway and reaches a speed of 80 m/s in 20 seconds. What is its acceleration?

a = vf – vi

ta = (80 m/s – 0 m/s)

20 sa = 80 m/s

20 sa = 4 m/s/sa = 4 m/s2

Calculating - Acceleration:

a = vf – vi

t Objects slow

down

A skateboarder is moving in a straight line at a constant speed of 3 m/s and comes to a stop in 2 seconds. What is his acceleration?

a = vf – vi

ta = (0 m/s – 3 m/s)

2 sa = -3 m/s

2 sa = -1.5 m/s/sa = -1.5 m/s2