Conservation of Energyand Momentum

Conservation

• If you gave me a dollar and asked for change, how many dimes would you want back?

• How about quarters?

Conservation

• In this example, money is CONSERVED. The amount did not change, only the form.

Conservation

• Energy, Momentum and Mass are just a few of the Physics quantities that are CONSERVED.

Conservation of Mass

• What would happen if you had a 10 gram ball of play-doh, then divided that ball into 2 pieces. Did the total mass stay the same?

• Let’s watch!

Conservation of Energy

• Energy causes things to happen. During the day, the sun gives off light and heat energy. At night, street lamps convert electrical energy to light. Our bodies convert the chemical energy in food into the kinetic energy we need to stay active

Energy Conversion

• What other types of energy conversion can you think of that are important to our environment?

Energy and Work• Energy is defined as the ability to do

work or cause change in the speed, direction, shape or temperature of an object.

• Work is done when a force causes an object to move.

• There is a very close relationship between work and energy.

• They are both measured in Joules.

Energy

• There are many different forms of energy. The energy we typically work with is called mechanical energy. It is divided into two main types:

• Potential Energy

• Kinetic Energy

Potential Energy• Potential Energy is the energy that is

stored. (energy of position or height)

• If you stretch a rubber band, you will give it potential energy. As the rubber band is released, potential energy is changed to motion.

• Gravitational Potential Energy is the energy stored in an object as the result of its height. The higher the object, the greater its potential energy.

• There is a relationship between the mass of an object and its gravitational potential energy. The more massive an object, the greater its potential energy.

• The formula to find gravitational PE is PE = mgh

Kinetic Energy• Kinetic Energy is energy that is

moving • A rubber band flying through the air, a bouncing

ball, and a roller coaster going down a track all have kinetic energy

• Kinetic energy is related to both mass and speed. The greater the mass or speed of an object, the greater the energy.

• Kinetic energy comes in different forms: electrical energy, mechanical energy, heat energy and chemical energy.

• The formula to find KE is KE = ½mv²

Conversion

• Potential Energy is converted into kinetic energy.

• Example: A waterfall has both potential and kinetic energy. The water at the top of the waterfall has potential energy. When the water begins to fall, its potential energy is changed into kinetic energy. This change in energy happens at Niagra Falls where it is used to provide electricity from the transformation of mechanical and electromagnetic energy to parts of the US.

Energy Conservation

• When you drop a ball, the potential energy is changed into kinetic energy. When the ball bounces to a lower and lower height, it is not losing energy. As the falling ball rubs against the air, some of the KE is turned into heat. Some energy changes into sound. Because some energy becomes unusable when it changes from one form to another, the ball will never have enough energy to bounce back up to its starting height.

Law of Conservation of Energy

• Energy can be neither created nor destroyed, but it can be converted from one form to another and it can be transferred from one object to another.

Exit

• In your notebook:

• Write the definition of potential energy and give an example

• Write the definition of kinetic energy and give an example

• Write the Law of Conservation of Energy and give an example’