warm-up: energy review answer the questions below. answer the questions below. 1. 2. 3

Warm-UpWarm-Up: Energy : Energy ReviewReview Answer the questions below.Answer the questions below.

1.

2.

3.

Where does the car have Where does the car have the most potential the most potential energy?energy?

1.1. Between A and Between A and BB

2.2. Between B and Between B and CC

3.3. Between C and Between C and DD

4.4. After DAfter D

Where does the car have Where does the car have more kinetic energy than more kinetic energy than potential?potential?

1.1. AA

2.2. BB

3.3. CC

4.4. DD

Force & Force & MotionMotion

MotionMotion

SpeedSpeed = rate at which an object = rate at which an object movesmoves

MotionMotion

SpeedSpeed = rate at which an object moves = rate at which an object moves

speed equation:speed equation: speed = distance speed = distance ÷ ÷ timetime

((v = d ÷ tv = d ÷ t))

units of speed:units of speed: meters per second (meters per second (m/sm/s) ) or or kilometers per hour kilometers per hour ((km/hrkm/hr))

ExampleExample: : A jogger runs the first 1000 m of a race A jogger runs the first 1000 m of a race in 250 sec. What is the jogger’s speed?in 250 sec. What is the jogger’s speed?

What is the correct way to plug in the What is the correct way to plug in the numbers?numbers?1.1. v = 250 sec v = 250 sec ÷ 1000 ÷ 1000

mm

2.2. v = 1000 m v = 1000 m ÷ 250 ÷ 250 secsec

3.3. v = 1000 m xv = 1000 m x 250 250 secsec

4.4. v = 250 sec xv = 250 sec x 1000 1000 mm

MotionMotion

SpeedSpeed = rate at which an object moves = rate at which an object moves

speed = distance speed = distance ÷ time ÷ time (v = d ÷ t)(v = d ÷ t)

ExampleExample::A jogger runs the first 1000 m of a race A jogger runs the first 1000 m of a race in 250 sec. What is the jogger’s in 250 sec. What is the jogger’s speed?speed?

v = 1000 m ÷ 250 sec.v = 1000 m ÷ 250 sec.

ExampleExample: : A jogger runs the first 1000 m A jogger runs the first 1000 m of a race in 250 sec. of a race in 250 sec. What is the What is the jogger’s speed?jogger’s speed?

1.1. 0.25 m/sec0.25 m/sec

2.2. 0.25 sec/m0.25 sec/m

3.3. 4 m/sec4 m/sec

4.4. 4 sec/m4 sec/m

MotionMotion

SpeedSpeed = rate at which an object moves = rate at which an object moves

speed = distance speed = distance ÷ time ÷ time (v = d ÷ t)(v = d ÷ t)

ExampleExample::A jogger runs the first 1000 m of a race A jogger runs the first 1000 m of a race in 250 sec. What is the jogger’s in 250 sec. What is the jogger’s speed?speed?

v = 1000 m ÷ 250 sec.v = 1000 m ÷ 250 sec.v = 4 m/sec.v = 4 m/sec.

MotionMotion

Speed Speed = rate at which an object moves= rate at which an object moves

VelocityVelocity = speed with a specific = speed with a specific directiondirection

ExampleExample: : A running back moves towards the A running back moves towards the east end zone at 10 m/sec. What is the east end zone at 10 m/sec. What is the running back’s running back’s velocityvelocity??

1.1. 10 m/sec10 m/sec

2.2. 10 m/sec west10 m/sec west

3.3. 10 m/sec east10 m/sec east

4.4. 10 meters east10 meters east

MotionMotion

SpeedSpeed = rate at which an object moves = rate at which an object moves

VelocityVelocity = speed with a specific direction = speed with a specific direction

ExampleExample::A running back moves towards the east end A running back moves towards the east end zone at 10 m/sec.zone at 10 m/sec.

– What is the running back’s What is the running back’s velocity?velocity?

velocity = 10 m/sec. eastvelocity = 10 m/sec. east

MotionMotion

AccelerationAcceleration = change in = change in velocityvelocity

MotionMotion

AccelerationAcceleration = change in = change in velocityvelocity– Acceleration can mean:Acceleration can mean:

Speeding upSpeeding up

MotionMotion

AccelerationAcceleration = change in = change in velocityvelocity– Acceleration can mean:Acceleration can mean:

Speeding upSpeeding up

Slowing downSlowing down

MotionMotion

AccelerationAcceleration = change in = change in velocityvelocity– Acceleration can mean:Acceleration can mean:

Speeding upSpeeding up

Slowing downSlowing down

Changing directionChanging direction

– Think of a Think of a rollercoasterrollercoaster because it because it can do all three!can do all three!

Which car is not Which car is not accelerating?accelerating?

1.1. A car driving up a hill A car driving up a hill and down the other side.and down the other side.

2.2. A car turning a corner.A car turning a corner.

3.3. A car turning a corner at A car turning a corner at a constant speed.a constant speed.

4.4. A car driving at a A car driving at a constant speed along a constant speed along a straight highway.straight highway.

Which is NOT an Which is NOT an example of example of acceleration?acceleration?

1.1. As you see your As you see your friend, you jump up friend, you jump up and run to greet and run to greet them.them.

2.2. Your dog runs in Your dog runs in circles chasing his tail.circles chasing his tail.

3.3. You pedal your bike You pedal your bike along your street at 5 along your street at 5 km/hr.km/hr.

4.4. A car slows down as it A car slows down as it comes to a red light. comes to a red light.

MotionMotion

AccelerationAcceleration = change in velocity = change in velocity

acceleration equation:acceleration equation: acceleration = velocity acceleration = velocity ÷ time÷ time ( (a = v ÷ ta = v ÷ t))

units of acceleration:units of acceleration: m/s per second (m/s per second (m/sm/s22) )

or or km/hr per hour (km/hr per hour (km/hrkm/hr22))

Example:Example: A car accelerates from 0 to 72 km/hr in 8 A car accelerates from 0 to 72 km/hr in 8 sec. What is the car’s acceleration?sec. What is the car’s acceleration?

What is the correct way to plug in the What is the correct way to plug in the numbers?numbers?1.1. a = 72 km a = 72 km ÷ 8 sec÷ 8 sec

2.2. a = 0 km/hr a = 0 km/hr ÷ 8 ÷ 8 secsec

3.3. a = 72 km/hr a = 72 km/hr ÷ 8 ÷ 8 secsec

4.4. a = 8 sec ÷ 72 a = 8 sec ÷ 72 km/hrkm/hr

MotionMotion

AccelerationAcceleration = change in velocity = change in velocity

acceleration = velocity acceleration = velocity ÷ time÷ time (a = v ÷ t) (a = v ÷ t)

Example:Example:A car accelerates from 0 to 72 km/hr in A car accelerates from 0 to 72 km/hr in 8 sec. What is the car’s acceleration?8 sec. What is the car’s acceleration?

a = 72 km/hr ÷ 8 sec. a = 72 km/hr ÷ 8 sec.

Example:Example: A car accelerates from 0 to 72 A car accelerates from 0 to 72 km/hr in 8 sec. km/hr in 8 sec. What is the car’s What is the car’s acceleration?acceleration?

1.1. 9 km/hr9 km/hr

2.2. 9 km/hr/sec9 km/hr/sec

3.3. 9 km/hr/hr9 km/hr/hr

4.4. 9 km9 km

MotionMotion

AccelerationAcceleration = change in velocity = change in velocity

acceleration = velocity acceleration = velocity ÷ time÷ time (a = v ÷ t) (a = v ÷ t)

Example:Example:A car accelerates from 0 to 72 km/hr in A car accelerates from 0 to 72 km/hr in 8 sec. What is the car’s acceleration?8 sec. What is the car’s acceleration?

a = 72 km/hr ÷ 8 sec. a = 72 km/hr ÷ 8 sec. a = 9 km/hr/sa = 9 km/hr/s

ForceForce

ForceForce = a = a pushpush or a or a pullpull

ForceForce

ForceForce = a push or a pull = a push or a pull

– forces have a forces have a strengthstrength and and directiondirection

– Forces are measured in units called Forces are measured in units called NewtonsNewtons ( (NN))

1 N 20 N

Small force pushing to the

right

Big force pushing to the left

ForceForce

BalancedBalanced forcesforces = = equal equal forces forces working on working on 11 object in object in opposite opposite directionsdirections

100 N100 NTotal force on rope = 0 N

Rope’s motion does not change (it is in equilibrium)

ForceForce

UnbalancedUnbalanced forcesforces = = unequalunequal forces cause an object to forces cause an object to accelerateaccelerate

120 N100 NTotal force on rope = 20 N to the right

Rope’s moves to the right (it is in disequilibrium)

Which box is Which box is experiencing unbalanced experiencing unbalanced forces?forces?

5 N10 N1.1. Box ABox A

2.2. Box BBox B

3.3. Box CBox C

4.4. Box DBox D

A

5 N

10 NB10 N

10 N C 10 N

10 ND5 N

5 N

What will Box D do?What will Box D do?

5 N10 ND5 N

1.1. Accelerate to the leftAccelerate to the left

2.2. Accelerate to the Accelerate to the rightright

3.3. Stay stillStay still

4.4. Explode Explode

Resistance ForcesResistance Forces

ResistanceResistance forcesforces = forces that = forces that go go againstagainst the the motionmotion of an of an objectobject

Which force is acting on the Which force is acting on the ball rolling across the ball rolling across the counter?counter?

1.1. Downward Downward force of gravityforce of gravity

2.2. Backward Backward force of frictionforce of friction

3.3. Upward force Upward force of the counterof the counter

4.4. All of these forces are All of these forces are acting on the ballacting on the ball

Resistance ForcesResistance Forces

Resistance forcesResistance forces = forces that = forces that go against the motion of an go against the motion of an objectobject– FrictionFriction = force exerted when 2 = force exerted when 2

surfaces surfaces rubrub against each other against each other

Resistance ForcesResistance Forces

Resistance forcesResistance forces = forces that = forces that go against the motion of an go against the motion of an objectobject– FrictionFriction = force exerted when 2 = force exerted when 2

surfaces rub against each othersurfaces rub against each other SlidingSliding = solid surfaces slide over each = solid surfaces slide over each

otherothermotion

friction

Resistance ForcesResistance Forces

Resistance forcesResistance forces = forces that = forces that go against the motion of an go against the motion of an objectobject– FrictionFriction = force exerted when 2 = force exerted when 2

surfaces rub against each othersurfaces rub against each other SlidingSliding RollingRolling = object rolls over a solid = object rolls over a solid

surfacesurface

F

M

Resistance ForcesResistance Forces

Resistance forcesResistance forces = forces that = forces that go against the motion of an go against the motion of an objectobject– FrictionFriction = force exerted when 2 = force exerted when 2

surfaces rub against each othersurfaces rub against each other SlidingSliding RollingRolling Fluid Fluid = object moving = object moving

through a fluid (through a fluid (liquid or gasliquid or gas))

Resistance ForcesResistance Forces

Resistance forcesResistance forces = forces that = forces that go against the motion of an objectgo against the motion of an object– FrictionFriction

SlidingSliding RollingRolling Fluid Fluid

– Force of friction depends on: Force of friction depends on: types of types of surfacessurfaces how how hardhard the surfaces push together the surfaces push together

When might you want When might you want to decrease friction?to decrease friction?

1.1. When driving on When driving on the highwaythe highway

2.2. When walking When walking across a wet flooracross a wet floor

3.3. When When snowboarding in snowboarding in the Olympicsthe Olympics

4.4. When climbing a When climbing a steep hillsteep hill

How could you How could you increase friction?increase friction?

1.1. Polishing metal Polishing metal surfacessurfaces

2.2. Adding oil to the Adding oil to the gears on a bikegears on a bike

3.3. Wearing slick Wearing slick shoes shoes

4.4. Putting sand on Putting sand on an icy drivewayan icy driveway

Resistance ForcesResistance Forces

Resistance forcesResistance forces = forces that = forces that go against the motion of an go against the motion of an objectobject– GravityGravity = force that = force that pullspulls objects objects

towardtoward each other each other

Resistance ForcesResistance Forces

Resistance forcesResistance forces = forces that = forces that go against the motion of an objectgo against the motion of an object– GravityGravity = force that pulls objects = force that pulls objects

toward each othertoward each other– Force of gravity Force of gravity

depends on:depends on: objects’ objects’ massmass distance between distance between

objectsobjects

Resistance ForcesResistance Forces

Resistance forcesResistance forces = forces that = forces that go against the motion of an go against the motion of an objectobject– Air resistanceAir resistance = a type of = a type of fluid fluid

friction that affects friction that affects fallingfalling objects objects

gravity

Air resistance

Resistance ForcesResistance Forces

Resistance forcesResistance forces = forces that = forces that go against the motion of an go against the motion of an objectobject– Air resistanceAir resistance = a type of fluid = a type of fluid

friction that affects falling objectsfriction that affects falling objects– Force of air resistance depends on:Force of air resistance depends on:

Object’s Object’s surface areasurface area Object’s Object’s speedspeed

gravity

Air resistance

When dropped, which When dropped, which object would experience object would experience the MOST air resistance?the MOST air resistance?

1.1. A flat sheet of A flat sheet of paperpaper

2.2. A wadded up A wadded up sheet of paper sheet of paper

3.3. A paperclipA paperclip

4.4. A tennis ballA tennis ball