# Chapter 4--Energy - PowerPoint PPT Presentation

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Chapter 4--Energy. The Nature of Energy. What is Energy — Energy is present all around us all day Energy changes are taking place constantly Ex: baseball flying and hitting a window, combing your hair, walking to class, etc. Energy is the ability to cause change

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Chapter 4--Energy

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### The Nature of Energy

• What is Energy—

• Energy is present all around us all day

• Energy changes are taking place constantly

• Ex: baseball flying and hitting a window, combing your hair, walking to class, etc

• Energy is the ability to cause change

• Anything that causes change must have energy

• There are many different forms of energy including electrical, chemical and thermal

### Kinetic Energy

• -is energy in the form of motion

• Ex: spinning wheel, sprinting runner, football passing through goalposts

• Amounts of Kinetic Energy depend on two quantities: mass and velocity

• (more mass = more energy)

• (more velocity = more energy)

### Potential energy

• -is stored energy due to position

• Objects that have potential energy have the ability to cause change

• Elastic Potential Energy= energy stored by something that can stretch or compress (ex: rubber band)

• Chemical Potential Energy = energy stored in chemical bonds (ex: atoms)

### Gravitational Potential Energy (GPE)

• Gravitational Potential Energy is energy stored by objects that are above Earth’s surface

• The amount depends on the MASS of the object, Acceleration Due to Gravity and HEIGHT above the ground

• GPE = mass X 9.8 m/s/s X height

• GPE is measured in Joules also

### There are many forms of energy:

• Electrical--movement of electrons

• Radiant--from the sun) electromagnetic energy

• Thermal –heat energy

• Chemical—stored in bonds of atoms and molecules

• Nuclear—stored in the nucleus of an atom

### Energy Conversions:

• Transforming electrical energy

• Happens all day, everyday

• Ex: lightbulbs transform electrical energy into light

• Some of the electrical energy is turned into thermal energy (hot bulbs)

• Other ex: alarm clock, straighteners, toaster, etc.

### Transforming chemical energy:

• Fuel is stored in the form of chemical potential energy

• Engines transform chemical potential energy stored in gas into kinetic energy

• Ex: a car engine—Fig. 7 in the textbook

• Green plants convert light energy from the Sun into stored energy in chemical bonds

### Conversions between kinetic and potential energy

• Many situations involve conversions between potential and kinetic energy

• Ex: bicycles, roller coasters, swings, etc.

• Mechanical energy is the total amount of potential and kinetic energy in a system

• Mechanical energy = GPE + KE

• When energy is transformed from potential to kinetic, the potential energy is not LOST, it has simply been converted, but the total amount of energy remains the same

• Ex:—apple tree, baseball, swing

### Law of Conservation of Energy:

• Kinetic and potential energy are constantly changing as the object speeds up and slows down

• However, mechanical energy stays constant

• So: -Energy cannot be created or destroyed, it simply changes form

### Friction and the Law of Conservation of Energy

• Friction slows moving objects, which seems to decrease mechanical energy of an object.

• However, friction converts energy to other forms such as thermal energy (heat)

### Converting Mass into Energy

• Nuclear fusion—a special kind of energy conversion

• During this process a small amount of mass is transformed into a tremendous amount of energy by fusing atomic nuclei (sun)

• Nuclear fission—similar process, but nuclei are broken apart, not fused together

### Human Body –Energy Conversions

• Complex chemical and physical processes in the body obey the law of conservation of energy

• Energy is stored as fat and converted to energy as needed for life processes

• 1 Calorie (C) is equal to 4,184 J

• Every gram of fat supplies 9 C of energy

• Section 2 Assessment questions