EnergyEnergy

Kinetic and PotentialKinetic and Potential

What is Energy?What is Energy?

The ability to do work. The ability to do work.

Work = Force X Distance

Forms of Energy:

Electrical Mechanical

Thermal Radiant

Gravitational Nuclear

The total amount of energy in a closed system is conserved. That is to say that energy can not be created nor destroyed, but can transform from one type of energy into another.

Examples:

rock falling down a hillside

solar energy changing to electrical energy

chemical energy changing to radiant energy

nuclear energy changing to thermal energy

Energy given to an object due to its position above the earth’s surface.

Potential EnergyPotential Energy

= Mass X Gravity X Height

Kinetic EnergyKinetic Energy

= ½ mass X Velocity2

Energy is measured in Joules!

Gravitational Potential Energy

= Mass ( Kg) X Gravity (9.8 m/s/s) X Height ( M )

How much potential energy would a 3 Kg rock have if it is placed on a hill that is 20 meters tall?

M = 3 Kg G = 9.8 m/s/s

H = 20 meters

PE = 3 Kg X 9.8m/s/s x 20 m

= 588 Joules = .588 Kjoules

Kinetic Energy =

½ Mass ( Kg) X Velocity2 (m/sec)

A 30 Kg athlete is running with a velocity of 18 m/sec toward the finish line, what is her kinetic energy?

M = 30 Kg V = 18 m/sec

KE = ½ 30 Kg x (18 m/sec)2

KE = 4860 Joules

Conservation of Potential Conservation of Potential EnergyEnergy

Since energy can Since energy can not be created nor not be created nor destroyed, an destroyed, an object with object with gravitational gravitational potential energy potential energy will transform that will transform that energy into kinetic energy into kinetic energy as it energy as it descends.descends.

Pendulum,Pendulum, device consisting of an object suspended from a fixed point that swings back and forth under the influence of gravity

High Kinetic

Zero Potential

High Potential

Zero Kinetic

High Potential

Zero Kinetic

A high diver in the circus, or a platform diver in the Olympics are great examples of the Law of Conservation of Energy. Imagine a 60 Kg diver at the top of a platform that is 20 meters above the pool. What are the potential and kinetic energies at 20 m, 15m, 10 m and 2 m above the pool?

20 M

15M

10M

2M

Complete the following Complete the following tabletable

Height above Height above the ground the ground (m)(m)

Potential Potential Energy Energy (Joules)(Joules)

Kinetic Energy Kinetic Energy (Joules) (Joules)

30 30

4,3124,312

00

A 30 Kg rock is dropped from a 30 meter tall cliff.

High jumpers are also great examples of the law of conservation of energy. The jumper starts with zero potential energy on the ground, but creates great kinetic energy by running toward the high jump bar.

The jumper then creates vertical lift and changes their kinetic energy into potential energy as she rises toward the peak of her jump.

KEi + PEi = KEf + PEf

Neglecting air resistance, a high jumper could use their top sprinting speed to determine how high they could jump.

If a 60 Kg athlete can run 8 m/sec, how high could they possibly jump off of the ground?

M = 60 Kg V = 8 m/sec

PEi = 0 Joules KEf = 0 joules

So: KEi = Pef

Therefore: ½ (60Kg) X (8m/sec)2

= 60Kg x 9.8 m/s/s x H

H = ½ (60 Kg) X (8 m/sec)2

/ 60 Kg x 9.8 m/s/s = 3.3 m

Pole VaultingPole Vaulting

Also an example of the law of Also an example of the law of conservation of energyconservation of energy

The pole is used as a means to The pole is used as a means to transfer energy from the athlete, transfer energy from the athlete, to the pole and finally back to the to the pole and finally back to the athleteathlete

The composition of the pole gives The composition of the pole gives definite advantage to the athletedefinite advantage to the athlete

kinetic

Potential

stored

Kinetic

Potential

http://www.polevaultpower.com/media/video/

http://www.neovault.com/

Roller coasters and many other amusement park rides are excellent examples of physics principles. In a 5 paragraph, typed essay describe the physics involved with a specific amusement park ride of your choice. Be sure to underline specific physics terms and references to physics principles or laws within your writing. Double space and use size 12 font. A full page labeled diagram should be included.

Use your knowledge of Newton’s Use your knowledge of Newton’s laws of motion, gravitational force, laws of motion, gravitational force, centripetal force and acceleration, centripetal force and acceleration, kinetic and potential energies.kinetic and potential energies.