Chapter 4 Section 1Energy

Page 99 - 105

Energy Definition

• Energy is the ability to cause change ????• Energy is the ability to do work.• Work is moving something against a force.

– Force and distance

• If we lift a block of metal from the floor to this table, we have done work on the block.– What is the force?

• If we push a box across the floor we do work.– What is the force

Different Types of Energy

• Mechanical • Electrical• Chemical• Sound• Light• Thermal (heat)• Nuclear

Energy Conversion• Chemical Energy to Mechanical Energy

– Burn gasoline in a car to make it go

• Chemical Energy to Electrical Energy– A battery supplies power to a cell phone

• Electrical Energy to Light Energy - ?• Electrical Energy to Sound Energy - ?• Electrical Energy to Mechanical Energy-? • Chemical energy to Thermal Energy• Electrical Energy to Thermal Energy

Kinetic Energy• The energy something has as a result of its motion

• KE = ½ m v2

• m = mass v = velocity

• v = 1 m/s v2= 1 m2/s2

• v = 2 m/s v2= 4 m2/s2

• v = 3 m/s v2= 9 m2/s2

• v = 4 m/s v2= 16 m2/s2

• v = 5 m/s v2= 25 m2/s2

Energy Units

• Energy is the same as work• KE= ½ m v2

– m in kg, v in m/s so v2 is m2/s2

– or (kg m/s2 )* m or N * m called a joule

• W = F d – F: Newtons Kg m/s2

– d : meters m– W : N m called a joule

• Kg m2 / s2 called a joule J

Practice Problems – Kinetic Energy(Page 102: 1,2,3)

• A jogger with a mass of 60.0 kg is moving at a speed of 3.0 m/s. What is the jogger’s kinetic energy?

• Given: • Asked:• Formula: KE = ½ mv2

• Substitute• Answer:

Page 102 Problem 1

• A baseball has a mass of 0.15 kg is moving at a speed of 40 m/s. What is the baseball’s kinetic energy

• Given: • Asked:• Formula: KE = ½ mv2

• Substitute• Answer:

Page 102 Problem 2

• A sprinter has a mass of 80.0 kg and a kinetic energy of 4,000 J. What is the sprinter’s speed?

• Given: • Asked:• Formula: KE = ½ mv2

• Substitute• Answer:

Page 102 Problem 3

• A car with a mass of 1,500 kg doubles its speed from 50 km/hr to 100 km/hr. By how many times does the kinetic energy of the car increase?

• Given: • Asked:• Formula: KE = ½ mv2

• Substitute• Answer:

Potential EnergyEnergy that is stored (available to do work)

• Examples–Elastic potential energy – stored in a spring–Chemical potential energy – stored in a

battery–Gravitational potential energy- stored by

an object due to its position above the Earth’s surface

Gravitational Potential energy

• The energy we store in an object when we lift it above the earth.

• GPE is equal to the work we do in lifting an object• work= Force x distance= Fg x h

• work = weight times the height• Since Fg = mg and height is the distance moved

• GPE = work done= mass x g x height• GPE= mgh kg x m/s2 x m = kg m2/s2

Practice Problems- Potential Energy Page 104: 1,2,3, 4EC

• What is the gravitational potential energy of a ceiling fan that has a mass of 7.0 kg and is 4.0 m above the ground?

• Given:• Asked:• Formula: GPE = mgh• Substitute:

• Answer:

Page 104 Problem 1

• Find the GPE of a coffee mug with a mass of 0.3 kg that is on a counter top 1m above the ground.

• Given:• Asked:• Formula: GPE = mgh• Substitute:

• Answer:

Page 104 Problem 2

• How high above the ground is a baseball with a mass of 0.15 kg and GPE of 73.5 J?

• Given:• Asked:• Formula: GPE = mgh• Substitute:

• Answer:

Page 104 Problem 3

• A rock climber is 200m above the ground and has a GPE of 117,600 J. What is the rock climber’s mass?

• Given:• Asked:• Formula: GPE = mgh• Substitute:

• Answer:

Page 104 Problem 4

• Suppose the mass of an object and it’s height above the ground both were doubled. How much would the object’s GPE change?

• Given:• Asked:• Formula: GPE = mgh• Substitute:

• Answer:

Different Types of Energy

• Mechanical • Kinetic Energy- due to motion• Gravitational Potential Energy- due to position

• Electrical• Chemical• Sound• Light• Thermal (heat) • Nuclear

Changes in Gravitational Potential Energy (page 105)

2 meters

2 meters

2 meters

2 meters

2 meters

Conservation of EnergySection 4:2 Page 107

Energy Transformation (P107)

Light Bulb

• Purpose is to convert electrical energy to light energy

• But, also bulb gets hot so we know that some of the energy has been converted to thermal energy (heat)

• Heat is wasted because the purpose is light• Fluorescent bulbs produce less heat so they

are more efficient.• What are some other devices that convert

electrical energy to some other form?

Energy Conversion• Chemical Energy to Mechanical Energy

– Burn gasoline in a car to make it go

• Chemical Energy to Electrical Energy– A battery supplies power to a cell phone

• Electrical Energy to Light Energy - ?• Electrical Energy to Sound Energy - ?• Electrical Energy to Mechanical Energy-? • Chemical energy to Thermal Energy• Electrical Energy to Thermal Energy

Chemical to Heat to Mechanical

Automobile Piston• Gas fumes and air are combined under pressure.• Spark from the plug ignites the fuel/air mixture.• Explosion exerts pressure pushing the piston

back down.• Changes chemical energy to heat energy to

mechanical energy.• A lot of energy is lost to heat so we have a

cooling system to remove this heat.

Conservation ofMechanical Energy

• Kinetic Energy is energy due to motion of an object.

KE = ½ m v2

• Potential energy is the energy due to position above the earth.

PE = mgh• Total Mechanical energy = KE + PE – wasted energy

Energy of a Projectile• Thrown (or hit) horizontally• Thrown (or hit) straight up• Thrown (or hit) up at an angle

Read Page 110

Cursive Writing

• I hereby agree to the conditions set forth in the test regulations and certify that I am the person whose name, address, and signature appear on the answer sheet.

• Name

Swing Energy (P110)

PE = maximumKE = 0

PE = minimumKE = maximum

PE = maximumKE = 0

BUT

• Will a swing swing forever?

Law of Conservation of Energy• Energy cannot be created or destroyed.• Energy changes form but is not created or

destroyed.• Total amount of energy in the universe does

not change.• We can add energy or take away energy from

a small part of the universe.• Energy in = energy out

– Hair Dryer (P111)

Swing Energy (P110)TME= GPE+KEGPE = ?KE = 0

TME= GPE+KEGPE = ?KE =

GPE = maximumKE = 0

Ground2 meters

14 meters

mass = 2 kg

Useless Energy

• As the swing moves, air resistance and friction convert some of the kinetic energy into thermal energy.

• The loss of thermal energy causes the swing to gradually slow down and stop.

Nuclear Energy (page 113)

• Prior to Einstein there were two separate laws– Conservation of Energy– Conservation of Mass

• Einstein E= mc2

Mass can be converted to energy and energy can be converted to mass

Nuclear FissionNuclear Fusion

Fission (splitting)

92 U235

54Xe140

38 Kr93

0n1

0n1

0n1

0n1

energy

Fusion (joining)

1H2 1H3

2He3

Chapter 4 Assignments

– Page 102: 1-2-3– Page 104: 1-2-3-4EC– Practice Problem Handout– Pendulum Lab- Monday 10/21– Note Taking Work Sheet Tue 10/22– Chapter 4 Review: 1-12, 22-25 Wed 10/23– Chapter 4 Test Thursday 10/24

Practice Problems• Find the kinetic energy of a ball with a mass of

0.75 kg moving with a speed of 50 m/s?• Find the gravitational potential energy of a 80 kg

diver on top of a 10m high diving tower?• If the diver jumps off the tower, what is the GPE of

the diver half way down to the water?• If the diver’s kinetic energy is 3920 Joules when he

is half way down, what is his velocity?• What will be the velocity of the diver just as he

hits the water? HINT: What will h = ?

Practice Problem 1Find the kinetic energy of a ball with a mass of

0.75 kg moving with a speed of 50 m/s?

• Given:• Asked:• Formula:• Substitute:• Answer

Practice Problem 2 Find the gravitational potential energy of a 80

kg diver on top of a 10m high diving tower?

• Given:• Asked:• Formula:• Substitute:• Answer

Practice Problem 3 If the diver jumps off the tower, what is the GPE of the diver half way down to the water?

• Given:• Asked:• Formula:• Substitute:• Answer

Practice Problem 4If the diver’s kinetic energy is 3920 Joules when

he is half way down, what is his velocity?

• Given:• Asked: units• Formula:• Substitute• Answer with units:

Problem 5

• What will be the velocity of the diver just as he hits the water? HINT: What will h = ?

• Given:• Asked: units• Formula:• Substitute• Answer with units:

Chapter 4 Assignments• Clear Desks except for calculator and Reference

Sheet• Write this formula on your Reference Sheet

Total Mechanical Energy = KE + GPE• Turn in homework before you leave

– Page 102: 1-2-3– Page 104: 1-2-3-4EC– Practice Problem Handout– Pendulum Lab– Note Taking Work Sheet– Chapter 4 Review: 1-12, 22-25

Problems

• Given:

• Asked: Units

• Formula: KE = 1/2mv2 , GPE= mgh, TME=KE+PE

• Substitute:• Answer: