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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