Goals Relate transformations and flow of energy within a system-chemical, mechanical, electromagnetic, light, sound, thermal, electrical, and nuclear. Identify energy transformations within a system (e.g. lighting of a match).

THE ABILITY TO CAUSE CHANGE ENERGY Sound THE ABILITY TO CAUSE CHANGE

The Joule (J) is the SI unit of Energy. Unit for Energy The Joule (J) is the SI unit of Energy. And is defined as a force of one newton is applied over a displacement of one meter 1J= 1N●m

Types of Energy mechanical energy

Heat energy -transfer of thermal energy Types of Energy Thermal energy - due to temperature (recall that this comes from the motion of molecules, so it is really kinetic energy) Heat energy -transfer of thermal energy Chemical Potential Energy - stored in chemical bonds Nuclear energy - stored in the nuclei of an atom Electrical energy - EM interactions Radiant energy -carried by EM waves

What types of energy are seen here?

Energy CLIP Energy is the capacity (ability) to do work. Potential Energy: Present in an object that has the potential to move because of its position Kinetic Energy: Associated with an object in motion

Potential and Kinetic Energy

Kinetic Energy the mass (m) of the object the speed (v) of the object. Motion KE of an object depends upon two variables: the mass (m) of the object the speed (v) of the object.

Calculating Kinetic Energy A formula to find the kinetic energy of any body based on its velocity.

The Unit for Kinetic Energy is the Joule  

Example Problems Kinetic Energy (KE = ½ m v2) 1) The velocity of a car is 65 m/s and its mass is 2515 kg. What is its KE?   2) If a 30 kg child were running at a rate of 9.9 m/s, what is his KE?

Practice Problems Page 2 #’s 1-7 Don’t do #5

What is the kinetic energy of a 55 kg object moving at 13 m/sec? KE = 2. A 6 kg rock is thrown with a velocity of 20 m/sec. What is the kinetic energy of the rock? m = v = KE =

3. When a golf ball is hit, it travels at 41 meters per second 3. When a golf ball is hit, it travels at 41 meters per second. The mass of a golf ball is 0.045 kg. What is the kinetic energy of the golf ball? m = v = KE = 4. A ball has 475 J of energy while in motion. If the ball is moving at 30 m/sec, what is the mass of the ball? m = v = KE =

6. Susie Maroney from Australia set a women’s record in long-distance swimming by swimming 93.625 m in 24.00 h. If Maroney’s mass was 55 kg, what was her kinetic energy?(Assume her velocity is equal to her average speed) m = v = KE = 7. In 1994, Leroy Burrell of the United States set what was then a new world record for the men’s 100 m run. He ran the 100 m distance in 9.85 s. Assuming that he ran with a constant speed equal to his average speed, and his kinetic energy was 3400 J, what was Burrell’s mass? m = v = KE =

An object has a kinetic energy of 88 J and a mass of 45 kg , how fast is the object moving? KE = An object has a kinetic energy of 14 J and a mass of 17 kg , how fast is the object moving? m = v = KE =

Potential Energy An object can store energy as the result of its position. Clip

Potential and Kinetic Energy

Forms of potential energy Gravitational Elastic Chemical -position above the Earth’s surface -stored in something stretchy -chemical reaction

Gravitational Potential Energy GPE is the energy stored in an object as the result of its vertical position (i.e., height). Amt. of GPE is dependent on two variables: the mass the height

Calculating Gravitational Potential Energy GPE = mgh

 

Elastic Potential Elastic PE is the energy stored in elastic materials as the result of their stretching or compressing.

Practice Problems Page 2 #’s 8-15

8. A man lifts a box with a mass of 13kg to a height of 12m 8. A man lifts a box with a mass of 13kg to a height of 12m. What is the potential energy of the box? m = g = h = GPE = 9. What is the coaster’s potential energy at position “A”? m = g = h = GPE =

10. What is the cup’s potential energy? m = g = h = GPE = 11. Ms. Andrews’s cat, Monkey, who has a mass of 6.4 kg, has climbed on top of the house to bird watch. If the house is 6.0 m tall, what is Monkey’s potential energy? m = g = h = GPE =

12. A cart at the top of a 300 m hill has a mass of 40 kg 12. A cart at the top of a 300 m hill has a mass of 40 kg. What is the cart’s gravitational potential energy? m = g = h = GPE = 13. A boulder has 6000 J of potential energy while sitting on top of a cliff. If the cliff is 210 m above the ground, what is the mass of the boulder? m = g = h = GPE =

14. An apple in a tree has a gravitational potential energy of 175 J and a mass of 0.36 g. How high from the ground is the apple? m = g = h = GPE = 15. A 50 N object is lifted to a height of 3 meters. What is the potential energy of this object? (hint: remember that Newtons is weight…compare the formula for weight and the formula for GPE) W= h = GPE =

Conservation of Energy

Conservation of Energy Energy cannot be created or destroyed…only changed from one form to another. The total energy of an isolated system remains constant (isolated systems have no external forces and no mass changes)

ENERGY BEFORE = ENERGY AFTER Energy can be changed from one form to another, but it does not disappear.

Conservation of Energy

Conservation of Energy TOTAL ENERGY OF THE SYSTEM REMAINS THE SAME Tutor Vista Activity (click)

TOTAL ENERGY OF THE SYSTEM REMAINS THE SAME Conservation of Energy KEi + PEi = KEf + PEf TOTAL ENERGY OF THE SYSTEM REMAINS THE SAME

Conservation of Mechanical Energy: KEi + PEi = KEf + PEf Problem: A student lifts his 2.0 kg pet rock 2.8 m straight up. He then lets it drop to the ground. Calculate the following: How much Potential Energy does it have at the top (before he drops it). How much Kinetic Energy does it have at the top (before he drops it). After it is dropped, how much KE will it have when it is 1.4 m above the ground? Total=54.88 54.88 = PEf + KEf 54.88 = mgh + KEf 54.88 = (2) (9.8)(1.4) + Kef 54.88 =27.44 + KEf 27.44 J = KEf 54.88 J 0 J

Conservation of Mechanical Energy: Conservation of ME only hold true when the only energies of the system are KE and PE. Therefore, in the presence of friction energy is transformed to other types of energies.

Tutor Vista Activity (click)

Examples 21 Lighting a Match Steam Engine Battery Can you think of More? ENERGY PROJECTS

What happens when it hits the ground? Where did the energy all go?

As it is falling and when the object hits the ground the energy is converted into other types of energy such as: sound energy (waves), Light Energy (sparks), thermal energy due to friction (heat) in the ground and air, vibrations in the earth (energy waves.) If the object bounces, some energy is converted momentarily into elastic potential energy.

EOCT Questions Which statement about energy is true? A Energy can be increased in a closed system. B Energy cannot be conserved. C Energy can be decreased in a closed D Energy cannot be created nor destroyed.

Wile E Coyote & Roadrunner Clip