Potential and Kinetic Energy

What is Energy? What does it mean if you have a lot of energy? For students it means you can run around, lift weights and scream. If you have energy you can do things. http://www.nv.doe.gov/news&pubs/photos&films/atm.htm

Energy is the ability to do work What is Energy? Energy is the ability to do work This is similar to our every day definition of energy. You can’t run up the stairs (work) without energy!

2)How is all energy divided? Potential Kinetic Gravitational Elastic Chemical

3)What is Potential Energy? Energy that is stored and waiting to be used later

4)What is Gravitational Potential Energy? Potential energy due to an object’s position Formula: GPE = mass x gravity x height Don’t look down, Rover! Good boy!

5)Examples of Gravitational Potential Energy A waterfall, a suspension bridge, and a falling snowflake all have gravitational potential energy.

With height! 6) How does GPE change? If you stand on a 3-meter diving board, you have 3 times the G.P.E, than you had on a 1-meter diving board. With height!

6) How does GPE change? “The bigger they are the harder they fall” is not just a saying. It’s true. Objects with more mass have greater G.P.E. So… WITH MASS

Let’s Practice A rock has a mass of 8.4 kg. The center of mass is 29.0 m above the ground. How much energy does it have? GPE = mgh We know: m= 8.4 kg g= 9.8 m/s2 h= 29.0 m GPE = (8.4kg)(9.8m/s2)(29m) = 2387.28 J

8) Elastic Potential Energy Potential energy due to compression or expansion of an elastic object. Notice the ball compressing and expanding

9) Chemical Potential Energy Potential energy stored within the chemical bonds of an object

10) Let’s take a 10 minute break and solve some problems! In the box, write ALL THE KNOWNS. Work on your own and make sure you get your teacher’s initials!

1) KINETIC ENERGY Energy of motion

2) Formula for KE KE = 0.5 mv2 Units: Joules (J) m = mass v = velocity

3) The energy of motion 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. Kinetic energy depends on both mass and velocity.

4) Let’s Practice What is the kinetic energy of this car when it is traveling 38.0 m/s? What other information do you need? KE = 0.5 m v2 Car’s mass = 1550kg

5) You practice now! The first 2 are kinetic, but be careful with the rest– they could be potential!

Energy: Forms and Changes

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.

Nature of Energy You use energy when you: hit a softball. lift your book bag. compress a spring.

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

Nature of Energy Energy is involved when: a bird flies. a bomb explodes. rain falls from the sky. electricity flows in a wire.

Nature of Energy What is energy that it can be involved in so many different activities? Energy can be defined as the ability to do work. If an object or organism does work (exerts a force over a distance to move an object) the object or organism uses energy.

Nature of Energy Because of the direct connection between energy and work, energy is measured in the same unit as work: joules (J). In addition to using energy to do work, objects gain energy because work is being done on them.

Forms of Energy Heat (Thermal) Chemical (food, fire, …) The five main forms of energy are: Heat (Thermal) Chemical (food, fire, …) Electromagnetic (electricity and magnetism) Nuclear (nuclear power, atomic bomb) Mechanical (motion and position of objects)

Heat Energy The internal motion of the atoms is called heat energy, because moving particles (kinetic energy) produce heat. Heat energy can be produced by friction. Heat energy causes changes in temperature and phase of any form of matter. As an object moves faster, it increases its thermal energy.

Chemical Energy Chemical Energy is required to bond atoms together. And when bonds are broken, energy is released.

Chemical Energy Fuel and food are forms of stored chemical energy.

Electromagnetic Energy Electromagnetic energy is a form of energy that travels through space in the form of waves. Power lines carry electromagnetic energy into your home in the form of electricity.

Electromagnetic Energy Light is a form of electromagnetic energy. Each color of light (Roy G Biv) represents a different amount of electromagnetic energy. Electromagnetic Energy is also carried by X-rays, radio waves, and laser light.

Nuclear Energy The nucleus of an atom is the source of nuclear energy.

Nuclear Energy When the nucleus splits (fission), nuclear energy is released in the form of heat energy and light energy.

Nuclear Energy The sun’s energy is produced from a nuclear fusion reaction in which hydrogen nuclei fuse to form helium nuclei. Nuclear energy is also released when nuclei collide at high speeds and join (fusion).

Mechanical Energy Mechanical energy is the energy associated with the motion and position of everyday objects. When work is done to an object, it acquires energy. The energy it acquires is known as mechanical energy.

Mechanical Energy When you throw a balling ball, you give it energy. When that bowling ball hits the pins, some of the energy is transferred to the pins (transfer of momentum). When you kick a football, you give mechanical energy to the football to make it move.

Mechanical Energy Mechanical energy is the sum of an object’s potential energy and kinetic energy. Mechanical Energy = Potential Energy + Kinetic Energy

What’s so important about PE and KE? We call the sum of PE and KE mechanical energy. ME = KE + PE Mechanical energy is important because it is conserved (as long as there are no non conservative forces, like friction) Therefore, if one goes down, the other goes up by the same amount.

States of Energy The most common energy conversion is the conversion between potential and kinetic energy. All forms of energy can be in either of two states: Potential Kinetic

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.

Kinetic vs. Potential Energy At the point of maximum potential energy, the car has minimum kinetic energy.

Kinetic-Potential Energy Conversions As a basketball player throws the ball into the air, various energy conversions take place.

Ball speeds up Ball slows down

Conceptual understanding A penny is dropped off the Eiffel tower (ignore air resistance). As it falls, what happens to it’s potential energy? What happens to it’s kinetic energy? As it falls, its velocity goes up, so its kinetic energy goes up. It also looses height so its potential energy goes down. However, mechanical energy stays the same ME = KE + PE

Energy Conversion Energy can be changed from one form to another. Changes in the form of energy are called energy conversions.

The Law of Conservation of Energy Energy can be neither created nor destroyed by ordinary means. It can only be converted from one form to another. If energy seems to disappear, then scientists look for it – leading to many important discoveries.

Law of Conservation of Energy In 1905, Albert Einstein said that mass and energy can be converted into each other. He showed that if matter is destroyed, energy is created, and if energy is destroyed mass is created. E = MC2

Energy conversions All forms of energy can be converted into other forms. The sun’s energy through solar cells can be converted directly into electricity. Green plants convert the sun’s energy (electromagnetic) into starches and sugars (chemical energy).

Other energy conversions In an electric motor, electromagnetic energy is converted to mechanical energy. In a battery, chemical energy is converted into electromagnetic energy. The mechanical energy of a waterfall is converted to electrical energy in a generator.

Energy Conversions In an automobile engine, fuel is burned to convert chemical energy into heat energy. The heat energy is then changed into mechanical energy.

Chemical  Heat Mechanical