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# Ch. 9 Motion - PowerPoint PPT Presentation

Ch. 9 Motion. Describing Motion Motion Speed & Velocity Acceleration. Newton’s First Law. Newton’s First Law of Motion An object at rest will remain at rest and an object in motion will continue moving at a constant velocity unless acted upon by a net force. motion. constant velocity.

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## PowerPoint Slideshow about ' Ch. 9 Motion' - roscoe

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### Ch. 9Motion

Describing Motion

Motion

Speed & Velocity

Acceleration

• Newton’s First Law of Motion

• An object at rest will remain at rest and an object in motion will continue moving at a constant velocity unless acted upon by a net force.

motion

constant velocity

net force

• Problem:

• We need a reference point...

• nonmoving point from which motion is measured

Motion

A. Motion

• Motion

• Change in position in relation to a reference point.

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.

v

t

B. Speed & Velocity

• Speed

• rate of motion

• distance traveled per unit time

• Instantaneous Speed

• speed at a given instant

• Average Speed

• 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

• speed in a given direction

• can change even when the speed is constant!

vf - vi

t

a

C. Acceleration

• Acceleration

• the rate of change of velocity

• change in speed or direction

a: acceleration

vf: final velocity

vi: initial velocity

t: time

• Positive acceleration

• “speeding up”

• Negative acceleration

• “slowing down”

t

v

D. Calculations

• Your 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

v = ?

WORK:

v = d ÷ t

v = (100 m) ÷ (20 s)

v = 5 m/s

You skate faster!

t

v

D. Calculations

• Sound 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:

v = 330 m/s

d = 1km = 1000m

t = ?

WORK:

t = d ÷ v

t = (1000 m) ÷ (330 m/s)

t = 3.03 s

vf - vi

t

a

D. Calculations

• A roller coaster starts down a hill at 10 m/s. Three seconds later, its speed is 32 m/s. What is the roller coaster’s acceleration?

GIVEN:

vi = 10 m/s

t = 3 s

vf = 32 m/s

a = ?

WORK:

a = (vf- vi) ÷ t

a = (32m/s - 10m/s) ÷ (3s)

a = 22 m/s ÷ 3 s

a= 7.3 m/s2

vf - vi

t

a

D. Calculations

• How long will it take a car traveling 30 m/s to come to a stop if its acceleration is -3 m/s2?

GIVEN:

t = ?

vi = 30 m/s

vf = 0 m/s

a = -3 m/s2

WORK:

t = (vf- vi) ÷ a

t = (0m/s-30m/s)÷(-3m/s2)

t = -30 m/s ÷ -3m/s2

t = 10 s

A

B

E. Graphing Motion

• slope =

• steeper slope =

• straight line =

• flat line =

speed

faster speed

constant speed

no motion

A

B

E. Graphing Motion

• 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

E. Graphing Motion

• Acceleration is indicated by a curve on a Distance-Time graph.

• Changing slope = changing velocity

E. Graphing Motion

• slope =

• straight line =

• flat line =

acceleration

• +ve = speeds up

• -ve = slows down

constant accel.

no accel. (constant velocity)

E. Graphing Motion

Specify 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

• Vectors measure using arrows to show direction and magnitude.

• Shows direction of the object's motion.

• Ex: velocity, acceleration, force. (all involve a direction)

• Principles:

• A glider moves through the air without the help of a motor or engine.

• A glider can move through the air and descend gradually when it is well designed and built.

• Think about aerodynamics to build a glider that will fly well. "Drag" "Thrust" "Lift" "Gravity“

• Facts:

• The design of your glider's body and wings has a lot to do with how well it will sail in the air.

• Adding some weight to parts of your glider will help it stay up in the air, have lift, and travel in a straight path instead of spinning or nosediving.