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ENERGY
Chapter 4
What is energy?
The ability to cause change
• Every change that occurs- large or small- involves energy.
• Anything that cause a change must have energy.
You need energy to breathe, yawn, open a book, write, throw a ball
The SI unit for energy is JOULES, abbreviated J
There are 4 different types of energy
1. Electrical
2. Chemical
3. Thermal
4. Radiant
Kinetic Energy
• The energy a moving object has because of its motion.
• The kinetic energy of a moving object depends on the objects mass
and its speed.
Find the Kinetic energy
1. What is the kinetic energy of a baseball moving at a speed of
40 m/s if the baseball has a mass of 0.15kg?
2. A car moving at a speed of 20 m/s has a kinetic energy of
300,000 J. What is the car’s mass?
3. A sprinter has a mass of 80 kg and a kinetic energy of 4,000 J.
What is the sprinters speed?
Potential Energy
• Stored energy due to its position
For example- A hanging apple in a tree has stored energy, and has the
ability to change.
Types Of Potential Energy
Elastic Potential Energy- energy stored by something that can stretch
or compress, such as a rubber band or spring.
Chemical Potential Energy- Energy stored in chemical bonds, such as
carbon and hydrogen together release gas when burned.
Gravitational Potential Energy-energy stored by objects due to
their position above the Earth’s surface.
On Earth the acceleration of Gravity is 9.8 m/s2 and has the symbol g
To calculate GPEGPE( J) = Mass(kg) X Acceleration of Gravity(m/s2) X Height (m)
1. What is the GPE of a ceiling fan that has the mass of 7kg
and is 4m above the ground?
Changing GPE
The GPE of an object can be increased by increasing its height above the ground.
• If two objects are at the same height, then the object with the larger
mass has more GPE.
Conservation of Energy
The changing forms of energy:
1. Transforming electrical energyA lightbulb is a device that transforms electrical energy into light energy
and thermal energy.
Transferring Chemical energy
• In the engine of a car, several energy conversions occur.
Conversions between Kinetic and Potential
Energy
• Mechanical energy is the total amount of potential energy and
kinetic energy in a system and can be expressed by this equation:
Mechanical energy= Potential energy + kinetic energy
In falling, projectile motion, and swings, kinetic and potential energy
are transformed into each other and the mechanical energy doesn’t
change.
THE LAW OF CONSERVATION OF ENERGY
• States that energy cannot be created or destroyed. This law means
that total amount of energy in theuniverse does not change.
Explain how this relates to a roller coater
• The effect of friction
Friction converts mechanical energy into thermal energy
Why do you rub your hands together when they are cold?
Nuclear fission
• A large amount of mass is transformed into an enormous quantity of
energy
Nuclear Fusion
A small amount of mass is transformed into a tremendous amount of
energy
The human body- balancing the energy
equation
What types of energy are formed in the human body?
-potential
-kinetic
-chemical
-thermal
Your body stores energy in the forms of fat and other chemical compounds.
To maintain a proper weight you must have a proper balance between
energy contained in the food you eat and the energy your body uses.
Food calories- a unit used to measure how much energy you get from certain foods.