Physical Science Coach Kelsoe Pages 444–468 C HAPTER 15: E NERGY

Physical Science Coach Kelsoe Pages 446–452 S ECTION 15–1: E NERGY AND I TS F ORMS

O BJECTIVES  Describe the relationship between work and energy.  Relate kinetic energy to mass and speed and calculate these quantities.  Analyze how potential energy is related to an object’s position and give examples of gravitational and elastic potential energy.  Solve equations that relate an object’s gravitational potential energy to its mass and height.  Give examples of the major forms of energy and explain how each is produced.

E NERGY AND W ORK  Remember from chapter 14 that work is done when a force moves an object through a distance.  Energy is the ability to do work. It is transferred by a force moving an object through a distance.  Work and energy are closely related. Work is a transfer of energy. Both work and energy are measured in joules (J), and a joule is a newton-meter.

K INETIC E NERGY  Many forms of energy can be classified into two general types: kinetic energy and potential energy.  The energy of motion is called kinetic energy. The Greek word kinetos means “moving.”  The kinetic energy of any moving object depends upon its mass and speed.  To calculate the kinetic energy of an object in joules, multiply the object’s mass in kilograms, the square of its velocity (speed) in meters per second, and ½. KE = ½mv 2

S AMPLE P ROBLEM – K INETIC E NERGY  A 0.10 kilogram bird is flying at a constant speed of 8.0 m/s. What is the bird’s kinetic energy?  Given: Mass: 0.10 kg Speed: 8.0 m/s  Solve: KE = ½mv 2 KE = ½(0.10 kg)(8.0 m/s) 2 KE = ½(0.10 kg)(64 m 2 /s 2 ) KE = 3.2 kgm 2 /s 2 KE = 3.2 J

P OTENTIAL E NERGY  Potential energy is the energy that is stored as a result of position or shape.  Pulling a string tightly before plucking it and holding a book in the air are examples of objects with potential energy.  There are two forms of potential energy: gravitational potential energy and elastic potential energy.

G RAVITATIONAL P OTENTIAL E NERGY  Potential energy that depends upon an object’s height is called gravitational potential energy. This type of potential energy increases when an object is raised to a higher level.  An object’s gravitational potential energy depends on its mass, its height, and the acceleration due to gravity. Remember that on Earth, g is always 9.8 m/s 2. GPE = mgh

S AMPLE P ROBLEM – P OTENTIAL E NERGY  Suppose a diver is at the top of a 10.0-meter-high diving platform has a mass of 50.0 kilograms. What is her gravitational potential energy?  Given: Height: 10.0 m Mass: 50.0 kg Gravity: 9.8 m/s 2  Solve: GPE = mgh GPE = (50.0 kg)(9.8 m/s 2 )(10.0 m) GPE = 4900 kgm 2 /s 2 GPE = 4900 J

E LASTIC P OTENTIAL E NERGY  The potential energy of an object that is stretched or compressed is known as elastic potential energy.  Something is said to be elastic of it springs back to its original shape after it is stretched or compressed.  When you drop a slice of bread on the ground, it may barely bounce. This is because it is not very elastic. When you drop a golf ball, it bounces almost back to where it was dropped from.

F ORMS OF E NERGY  All energy can be considered to be kinetic energy, potential energy, or the energy in fields such as those produced by electromagnetic waves.  The major forms of energy are mechanical energy, thermal energy, chemical energy, electrical energy, electromagnetic energy, and nuclear energy.

M ECHANICAL E NERGY  The energy associated with motion and position of everyday objects is mechanical energy.  Mechanical energy is not limited to machines. Mechanical energy is the sum of an object’s potential energy and kinetic energy.  Speeding trains, bouncing balls, and sprinting athletes all have mechanical energy.

T HERMAL E NERGY  Almost all of the matter around you contains atoms. These particles are always in random motion and thus have kinetic energy.  The total potential and kinetic energy of all the microscopic particles in an object make up its thermal energy.  When an object’s atoms move faster, its thermal energy increases and the object becomes warmer. If they get hot enough, they may emit visible light.

C HEMICAL E NERGY  Chemical energy is the energy stored in chemical bonds. When bonds are broken, the released energy can do work.  All chemical compounds, including fuels like coal and gasoline, store energy.  Burning wood at a campfire is considered chemical energy because the chemical bonds in the wood are being broken. This provides thermal energy to roast marshmallows!

E LECTRICAL E NERGY  Electrical energy is the energy associated with electric charges.  Batteries convert chemical energy into electrical energy.  Lightning bolts are produced by electrical energy.

E LECTROMAGNETIC E NERGY  Electromagnetic energy is a form of energy that travels through space in the form of waves.  X-rays and visible light are examples of electromagnetic energy.  Because they can travel long distances through air and space, they are often used in communication.

N UCLEAR E NERGY  The nucleus of an atom is held together by strong and weak nuclear forces, which can store an enormous amount of potential energy.  The energy stored in atomic nuclei is known as nuclear energy.  Nuclear fission and fusion are processes that create and use nuclear energy.

V OCABULARY  Energy  Kinetic energy  Potential energy  Gravitational potential energy  Elastic potential energy  Mechanical energy  Thermal energy  Chemical energy  Electrical energy  Electromagnetic energy  Nuclear energy