The Nature of Energy Chapter 4

What is energy? Energy is the ability to cause a change.

Kinetic Energy Kinetic energy – energy in the form of motion The amount of kinetic energy an object has depends on its mass and its speed

Kinetic Energy Kinetic energy – energy in the form of motion The amount of kinetic energy an object has depends on its mass and its speed Kinetic energy = ½ mass X speed2

Kinetic Energy Kinetic energy – energy in the form of motion The amount of kinetic energy an object has depends on its mass and its speed Kinetic energy = ½ mass X speed2 Joule – the SI unit used to measure energy

Potential Energy Potential Energy – energy stored in a motionless object, giving it the potential to cause change

Elastic Potential Energy Energy stored by things that stretch or compress

Chemical Potential Energy Energy stored in chemical bonds between atoms Example: Food you eat or Gasoline for your car

Gravitational Potential Energy Energy stored by things that are above the earth

Gravitational Potential Energy Energy stored by things that are above the earth The amount of GPE an object has depends on its mass, the acceleration due to gravity, and its height above the ground GPE = mass in kilograms X 9.8 m/s2 X height in meters

Gravitational Potential Energy GPE = mass X gravity X height Mass in kilograms Gravity in m/s2 height in meters GPE = mgh

Chapter 4 Section 2

Conservation of Energy

Conservation of Energy Energy Conservation – energy changing from one form to another

Conservation of Energy Energy Conservation– energy changing from one form to another Fuels store energy in the form of chemical potential energy

Conservation of Energy Energy Coservation – energy changing from one form to another Fuels store energy in the form of chemical potential energy Mechanical Energy – the total amount of potential and kinetic energy in a system ME = PE + KE

Law of Conservation of Energy Law of conservation of Energy – energy may change from one form to another, but the total amount of energy never changes Example – as a swing moves back and forth, its energy continually converts from kinetic to potential energy and back

Law of Conservation of Energy Law of conservation of Energy – energy may change from one form to another, but the total amount of energy never changes Example – as a swing moves back and forth, its energy continually converts from kinetic to potential energy and back If the energy of the swing decreases, then the energy of some other object must increase by an equal amount Friction converts some of the mechanical energy into thermal energy

Converting mass into energy…

Converting mass into energy… Nuclear energy – you must think of mass as energy when discussing nuclear reactions. The total amount of mass and energy is conserved Nuclear fusion – two nuclei are fused together – takes place in the sun Nuclear fission – nuclei is broke apart

Conservation of Energy… In your body??? Stored chemical PE changes to KE… keeps your body at a certain temp (thermal energy) Chemical potential energy from food that is stored in your body is used to fuel the processes that keep you alive

Calories Used in 1 hour of… Type of Activity Small body frame Medium Body Frame Large body frame Sleeping 48 56 64 Sitting 72 84 96 Eating 98 112 Standing 123 Walking 180 210 240 Playing Tennis 380 420 460 Bicycling (fast) 500 600 700 Running 850 1,000

What is a calorie? A food calorie is used to measure how much energy you get from various foods. Food energy is measured in joules in the SI system. The standard energy unit used by nutritionists in the United States is the Calorie. One Calorie (with a capital “C”) is also known as a kilocalorie and is equal to 1000 calories (lower case “c”). One calorie is equal to 4.184 joules. calorie = 4.184 joules Calorie = 4,184 joules