Catalyst

• What is Newton’s 3 rd example of the law? Law? Give me an

Kinetic and Potential energy

Page 447

Go over homework

• Pg 377 Data analysis • Pg 377 questions 1-7

• Energy: the ability to do work • work is a transfer of energy • measured in Joules= kgm 2 /s 2

Kinetic Energy

• the energy of motion • kinetic energy of any moving object depends upon its mass and speed – equation: Kinetic energy= half the mass times the velocity squared » KE= ½ mv 2 http://www.brainpop.com/science/energy/kin eticenergy/preview.weml

Practice Problem

• A 0.10 kg bird is flying at a constant speed of 8.0 m/s. What is the bird’s kinetic energy?

More Practice Problems

• • • • A 20kg dog is running at a constant speed of 16 m/s. What is the dog’s kinetic energy?

A 50 kg human is walking at a constant speed of 4 m/s. What is the human’s kinetic energy?

A human has a kinetic energy of 3.1 J, and a speed of 2.7m/s. What is the human’s mass?

A car has a kinetic energy of 6.3 J, and a speed of 5.4 m/s. What is the car’s mass?

Potential Energy

• energy that is stored as a result of position or shape. http://www.brainpop.com/science/energy/pot entialenergy/preview.weml

Gravitational Potential Energy

• potential energy that depends upon an object’s height • an object’s gravitational potential energy depends on its mass, its height, and the acceleration due to gravity. – Potential energy (PE) = mgh – g (on earth) = 9.8 m/s (N)

Practice Problem

• Suppose the diver at the top of a 10.0 meter high diving platform has a mass of 50.0 kilograms. You can calculate her potential energy relative to the ground.

More Practice Problems

• • • • A bird is sitting on top of a 17 meter high tree branch. The bird has a mass of 2 kg, what is its potential energy relative to the ground?

A jaguar is sitting on a tree branch 4.3 meters from the ground, waiting to attack its prey. The jaguar weighs 89kg, what is its potential energy relative to the ground?

The potential energy for a 2.5 kg squirrel in the tree is 1,500 J. At what height is the squirrel at?

The potential energy for a diver is 4,900 J. The diver is on top of a 15 meter high diving board. What is the mass of the diver?

Other Forms of Energy

• Mechanical energy: energy associated with the motion and position of everyday objects • the sum of the potential and kinetic energies – example: bouncing a ball, speeding trains etc

Homework

• Create a comic strip that either discusses the differences between – Kinetic energy and potential energy (include equations) – Newton’s 3 laws of motion

• Thermal Energy: • The total potential and kinetic energy of all the microscopic particles in an object.

– example: when an object’s atoms move faster, it’s thermal energy increases and the object becomes warmer

Elastic Potential Energy

• The potential energy of an object that is stretched or compressed – Normally springs back to its original state

• Chemical energy: • energy stored in chemical bonds – burning gasoline

• Electrical energy: • energy associated with electrical charge – ex flashlights, cds

• Electromagnetic energy: • energy that travels through space in the form of waves – ex galaxies

• Nuclear energy: • energy stored in atomic nuclei – nuclear fission or nuclear fusion Practice problems: • Questions 6-9 pg 452

Exit Ticket

• Name and explain all of the energies needed to heat a cup of water

Conservation of energy

Page 453

Conservation of Energy

• Energy can be converted from one from to another • Energy conversion: the process of changing energy from one form to another.

• The law of conservation of energy states that energy cannot be created or destroyed

• Gravitational potential energy of an object is converted to the kinetic energy of motion as the object falls

Energy conservation Equations

• • • • Mechanical energy = KE + PE (KE + PE)beginning = (KE + PE) end KE beginning = PE end PE beginning = KE end

Practice Problem

• At a construction site, a 1.50 kg brick is dropped from rest and hits the ground at a speed of 26.0 m/s. Assuming air resistance can be ignored, calculate the gravitational potential energy of the brick before it was dropped

More Practice Problems

• At a playground, a 3.4 kg ball is dropped from rest and hits the ground at a speed of 28 m/s. Assuming air resistance can be ignored, calculate the gravitational potential energy of the ball before it was dropped. • At a hospital, a 1.8 kg stethoscope is dropped from rest and hits the ground at a speed of 14 m/s. Assuming air resistance can be ignored, calculate the gravitational potential energy of the stethoscope before it was dropped.

• • Einstein’s equation E =

mc

2 , says that energy and mass are equivalent and can be converted into each other. (c = speed of light 9 x 10 13 J energy is released as matter is destroyed, and matter can be created from energy.

Practice Problems

• 9 and 10 on page 459.

Finish Newton’s Laws

• Create a mini comic strip that explains and demonstrates – Newton’s 1 st , 2 nd , and 3 rd laws