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Chapter 4: Energy

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**Nature of Energy Energy is all around you!**

You can hear energy as sound. You can see energy as light. And you can feel it as wind.

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**Nature of Energy Energy is involved when: a bird flies.**

a bomb explodes. rain falls from the sky. electricity flows in a wire.

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**Living organisms need energy for growth and movement.**

Nature of Energy Living organisms need energy for growth and movement.

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Nature of Energy What is energy that it can be involved in so many different activities?

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Energy Energy can be defined as the ability to cause change.

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Energy Unit of Measure ALL forms of energy is measured in units called joules.

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**Scientists refer to 2 types of energy**

Kinetic Energy Potential Energy

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What is kinetic energy?

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Kinetic Energy The energy of motion is called kinetic energy.

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**Kinetic Energy Kinetic energy depends on both mass and velocity.**

The faster an object moves, the more kinetic energy it has. The greater the mass of a moving object, the more kinetic energy it has.

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Let’s Look….. The vehicles below are traveling at the same velocity of 100 km/h. Do they have the same amount of kinetic energy? Why? Why not?

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Answer No, the kinetic energy is different for each vehicle. The truck has a GREATER mass than the motorcycle, so the truck has GREATER kinetic energy.

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**Formula for Kinetic Energy**

K.E. = mass x velocity2 2 K.E. = m X v2 What has a greater affect of kinetic energy, mass or velocity? Why? The velocity does because its value is squared!

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Let’s Practice.. Calculate the kinetic energy of a 3 kg rock that rolls down the hill with a velocity of 2 m/s. K.E. = m X v2 2

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Did you get…… Calculate the kinetic energy of a 3 kg rock that rolls down the hill with a velocity of 2 m/s. K.E. = 3 X 22 2 K.E. = 6 Joules

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Quiz Time! Show me what you have learned so far by answering the 4 questions that follow….

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Question 1 Which has more kinetic energy, a large dog sitting on a sidewalk or a small cat running down the street? The large dog The small cat Both have the same kinetic energy Need more information to answer

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Question 2 To what property of an object is kinetic energy directly related? Volume Height Position Mass

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Question 3 Observe the figure below. Which motorcycle has more kinetic energy? Assuming that the motorcycles have the same mass. Motorcycle A Motorcycle B Need more information B A

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Question 4 Elastic potential energy is measured in ________. Kilograms (kg) Newtons (N) Joules (J) Meters per second (m/s)

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**What is potential energy?**

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**Potential Energy Potential energy is stored energy due to position.**

Motionless objects have potential energy!

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**3 Types of Potential Energy**

Elastic Potential Energy Chemical Potential Energy Gravitational Potential Energy

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**Elastic potential energy- energy stored by something that can stretch or compress**

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**Chemical potential energy- energy stored in chemical bonds**

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**Gravitational Potential Energy: energy stored by objects ABOVE Earth’s surface**

Apple

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**Gravitational Potential Energy**

“The bigger they are the harder they fall” is not just a saying. It’s true! Objects with MORE mass have greater Gravitational potential energy (G.P.E.)

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**Gravitational Potential Energy**

G.P.E. depends on 3 things: 1. Mass of the object 2. Acceleration due to gravity = 9.8 m/s2 3. Height of the object

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**Formula for G.P.E. G.P.E. = mass X 9.8 m/s2 X height**

G.P.E = m X 9.8 m/s2 X h

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Let’s Practice.. What is the GPE of a 65 kg pole vaulter that is 15 m in the air? G.P.E = m X 9.8 m/s2 X h

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Did you get…… What is the GPE of a 65 kg pole vaulter that is 15 m in the air? G.P.E = 65 X 9.8 X 15 G.P.E. = 9555 J

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Quiz Time! Show me what you have learned so far by answering the 4 questions that follow….

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Question 1 The gravitational potential energy of an object depends on which of the following? Velocity and height Velocity and weight Weight and height Weight and acceleration

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**Question 2 A B Which vase has more gravitational potential energy?**

Vase A Vase B Can not determine Vase A and B have the same GPE A B

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Question 3 Green plants store energy from the Sun in what form? Light energy Elastic potential Gravitational potential energy Chemical potential

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**Question 4 Point A Point B Point C**

Observe the figure on the right. At which point would the roller coaster have the MOST potential energy? Point A Point B Point C A B C

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**Conservation of Energy**

Energy is most noticeable when it changes from one form to another! Think about it…..

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**Well, probably not until it fell, right?**

Would you…. Would you think that a book on top of a bookshelf as having much to do with energy? Well, probably not until it fell, right?

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Energy Tranforms….. Energy transforms from one form of energy to another form of energy. Let’s consider……The electrical energy from a light bulb is transformed into what types of energy? Electrical Energy Light Energy Thermal (Heat) Energy

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**Energy Transforms……….. Potential Energy Kinetic Energy**

Ball slows down Ball speeds up

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**Kinetic vs. Potential Energy**

At the point of maximum potential energy, the car has minimum kinetic energy.

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**Kinetic-Potential Energy Conversion**

Roller coasters work because of the energy that is built into the system. Initially, the cars are pulled mechanically up the tallest hill, giving them a great deal of potential energy. From that point, the conversion between potential and kinetic energy powers the cars throughout the entire ride.

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**The Law of Conservation of Energy**

Energy can not be created or destroyed it can only be converted from one form of energy to another. The total amount of energy in the universe remains constant!

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**Friction converts some mechanical energy to thermal (heat) energy.**

Rub your hands together. Feel it!

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Mechanical Energy Mechanical Energy – is the total amount of P.E. and K.E. in a system M.E. = Total P.E. + Total K.E.

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**Nuclear Fission = nuclei split apart (fission=division)**

Mass is converted to energy in the processes of fission and fusion. Nuclear Fission = nuclei split apart (fission=division) Nuclear Fusion = nuclei combine (fusion FUSE)

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The food calorie (C) is a unit used by nutritionists to measure how much energy you get from various foods. 1 calorie = joules Kilocalorie = Calorie

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Quiz Time! Show me what you have learned so far by answering the 4 questions that follow….

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Question 1 What energy transformations occur when a lump of clay is dropped? GPE KE thermal energy KE chem PE thermal energy KE GPE thermal energy GPE KE elastic PE

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Question 2 Suppose a juggler is juggling oranges. At an orange’s highest point, what form of energy does it have? Mostly potential energy Mostly kinetic energy No potential or kinetic energy Equal amounts of both

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Question 3 Which idea is central to the law of conservation of energy? Friction produces thermal energy People must conserve energy The total amount of energy is constant Energy is the ability to cause change

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Question 4 Friction frequently causes some of an object’s mechanical energy to be changed to which of the following forms? Thermal energy Nuclear energy Gravitational potential energy Chemical potential energy

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The End Be ready for TEST!

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