# Energy What do they all have in common?. Energy Defined as the ability to cause change!! Revisit the previous slide and explain how each of these has.

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Energy What do they all have in common?

Energy Defined as the ability to cause change!! Revisit the previous slide and explain how each of these has the ability to cause change!!

2 Types of Energy Kinetic Energy Energy of motion. – In order to have Kinetic energy an object must be in motion(It must have a velocity!! Potential Energy The energy of position or condition. Several kinds of Potential Energy: 1.Gravitational PE 2.Elastic PE 3.Chemical PE 4.Nuclear PE

Types of Potential Energy Gravitational Potential Energy(Pe g ) is the potential energy an object has due to its height. – The higher an object, the more potential it has to cause change!! Mr. Eidson Mr. Rodgers

Elastic Potential Energy is the potential energy an object has due to being stretched or compressed. Types of Potential Energy

Chemical Potential Energy is the potential energy something has because of its chemical makeup!! Types of Potential Energy(cont.) Sodium tossed into pond!

Nuclear Potential Energy is the potential energy of the particles inside an atomic nucleus. Types of Potential Energy(cont.)

Kinetic Energy Where: KE = kinetic energy in Joules(J) m = mass in kilograms(kg) v = velocity in m/s James Prescott Joule 1818-1889

Ex. A 1500 kg car moves down the road at 12 m/s. How much kinetic energy does the car have? Given: m = 1500 kg v = 12 m/s KE = ? KE = ½(1500kg)(12 m/s) 2 KE = 108,000 J

Ex. A 350 kg boulder is rolling down a hill at 17 m/s. How much kinetic energy does the boulder have? Given: m = 350 kg v = 17 m/s KE = ? KE = ½(350kg)(17 m/s) 2 KE = 50,575 J

A 1.5 kg football is thrown with a velocity of 15 m/s. What is the kinetic energy of the football? A. 11.25 J B. 22.5 J C. 168.8 J D. 337.5 J

A 2000 kg truck is moving down the highway at 8 m/s. What is the kinetic energy of the truck? A. 8000 J B. 16,000 J C. 64,000 J D. 160,000 J

Ex. A 3000 kg racecar has 200,000 J of kinetic energy as it moves around the track. Determine the velocity of the racecar? Given: m = 3000 kg v = ? KE = 200,000 J

Ex. A 25 kg rock is thrown with a velocity of 2 m/s. What happens to the kinetic energy of the rock if the velocity is doubled? Given: m = 25 kg v = 2 m/s KE = ? KE = ½(25kg)(2 m/s) 2 KE = 50 J KE = ½(25kg)(4 m/s) 2 KE = 200 J KE increases by a factor of 4!! ?

Gravitational Potential Energy(PE g ) PE g = mgh = F g h Where: PE g = Gravitational Potential Energy in Joules(J) m = mass is kilograms(kg) g = acceleration due to gravity(9.80 m/s 2 ) h = height in meters(m) F g = weight in Newtons(N)

If there are 2 equations, how do I know which one to use?? I don’t know, we should probably ask Hillary? She thinks she knows everything!!!

Well, if you’re given the mass(in kg), use PE g = mgh And if you’re given weight(in N), use PE g = F g h

Ex. A 450 kg boulder rests on the edge of a 120 m high cliff. Determine the gravitational potential energy of the boulder. Given: m = 450 kg h = 120 m g = 9.80 m/s 2 PE g = ? PE g = mgh PE g = 450(9.80)(120) PE g = 529,200 J

Ex. A 90 N flowerpot sits on the edge of a 14 m high window. How much potential energy does the flowerpot have? Given: F g = 90 N h = 14 m PE g = ? PE g = F g h PE g = 90 N(14 m) PE g = 1,260 J

Ex. To what height would you have to lift a 25 kg barbell to give it 612.5 J of potential energy? Given: m = 25 kg PE g = 612.5 J g = 9.80 m/s 2

A 4500 kg boulder rests on the edge of a 40 m high cliff. What is the potential energy of the boulder? A.180,000 J B.1,764,000 J C.260,000 J D.2,390,000 J

A 400 N box rests on a 2.5 m high cliff. What is the potential energy of the box? A.1000 J B.4800 J C.9800 J D.14,200 J

Is it possible for one type of energy to change to another type of energy? Consider the picture to the left: At point A, what type of energy does the ball have? Potential Only WHY? At point B, what type of energy does the ball have? Both PE and KE WHY?? At point C, what type of energy does the ball have? KE only WHY? How did this happen?

Tomorrow: You will design your own lab to answer the following question…….. “Is there a relationship between Gravitational Potential Energy and Kinetic Energy for a ball tossed into the air(A Free-Falling Body)? You will state a hypothesis(after discussion with your group), design an investigation, analyze data, state a conclusion!!!

Can other types of energy change?

WHY?

Where is PE and KE highest and lowest?

Rank Potential Energy from high to low! A-----C-------E----------D--------B Rank Kinetic Energy from high to low! B------D------E----------C--------A

Which Skier has the highest Potential energy?

Which skier has the highest kinetic energy?

Which Skier is moving the fastest?

Where is the potential energy the greatest?

Where is the potential energy the least?

Where is the kinetic energy the greatest?

Where is the kinetic energy the least?

Which rock is moving the fastest?

Law of Conservation of Energy As long as no unbalanced forces act on a system of objects, the total energy in a system will remain the same. Energy may change form, but it cannot be created nor can it be destroyed!!

Mechanical Energy remains Constant: Total Potential and Kinetic energy. – ADD THEM UP!!

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