CHAPTER 15 ENERGYSection 15.1Energy and Its Forms

15.1 Energy and Its Forms

•Underlying law of the universe “ The Law of Conservation of Energy”

• Energy (nrg) is continuously converting between many different forms.

• Energy is the ability to do work.• Energy is transferred by a force. ( Work and energy are closely related)

15.1 Energy and Its Forms

• When work is done on an object energy is transferred to the object.

• So work is a transfer of energy.• Work and energy units are J ( Joules)• What is food energy measured in? Calories

• Different types of calories.• Food Calories and heat calories.

15.1 Energy and Its Forms

• A food Calorie is equal to 1kcal or 1000 conventional calories (heat calories)

• A conventional calorie = 4.184 J • Can be converted to Joules. # of calories in food. SI unit C for food calories, heat calories c.

• Bodies goal is to burn off every calorie you take in.

15.1 Energy and Its Forms

•2 General Types of Energy • 1. Kinetic Energy - energy of motion • It depends on its mass and speed. • Formula: • KE= 1/2 mv2 • KE Kineitic Energy = half mass times velocity squared.

• KE = Joules• Mass =kg• Velocity Meters per second m/s

15.1 Energy and Its Forms

• Book problem page 448• Given• M =0.10kg bird• V=8.0 m/s• What is the bird’s kinetic energy?• Formula: KE= 1/2 mv2 • KE = ½ (0.10kg)(8.0m/s)2

• Solve either way • KE=1/2 ( 0.10kg) (64m2/s2 ) or KE = 0.5 ( 0.10kg) (64m2/s2

)•  =3.2 Kg × m2/s2

• =3.2 J

15.1 Energy and Its Forms

• 2. Potential Energy (PE) – is energy that is stored as a result of position or shape.

• It is basically energy with the potential to do work.

• Ex. Holding a book, a rock on a cliff• 2 forms of PE• 1. Gravitational PE• 2. Elastic PE

15.1 Energy and Its Forms

• 1. Gravitational PE – potential energy that depends on an objects height.

• It increases when a object is raised to a higher level

• Calculating Gravitational PE• Formula: PE = mgh• Remember from chapter 12 Weight = mg• m = mass and g= acceleration due to gravity.

15.1 Energy and Its Forms

• So often the formula for gravitational potential energy is written using weight and not with the mg.

• Potential energy general formula:• PE = wt x ht Weight x height.• PE units = Joules (J)• Weight = Newtons (N)• Height = meters (m)

15.1 Energy and Its Forms

• Sample Problem 1(using PE = mgh) : • A diver has a mass of 50.0 kg standing at the top of a 10.0 m diving platform. Calculate the PE relative to the ground.

• PE = mgh• PE = (50.0 kg)(9.8 m/s2)(10.0 m)• PE = 4900 kg• m2/s2

• PE = 4900 J

15.1 Energy and Its Forms

• Sample Problem 2 (using PE = wt • ht):• What is the potential energy of a 10 newton book that is placed on a shelf that is 2.5 meters high?

• PE = wt • ht• PE = (10 N)(2.5 m)• PE = 25 N • m, remember a N • m is= to a J• PE = 25 J

15.1 Energy and Its Forms

• 2. Elastic PE- the potential energy of an object that is stretched or compressed.

• An object is elastic if it springs back to its original shape after it is stretched or compressed.

• Ex: rubber band, slinky• Elastic PE can be stored in objects that are compressed like springs.

• Balls have compressed air in them.

15.1 Energy and Its Forms

Know the forms of energy.• Mechanical energy• Thermal energy• Chemical energy• Electrical energy• Electromagnetic energy• Nuclear energy• (make sure you write down each form in your notes and give an example of each)