Work Kinetic Energy Potential Energy What is Work

Work, Kinetic Energy, & Potential Energy

What is Work? • Work is… – the transfer of energy through motion – a force exerted on a body through a change in position • Work is done only when… – a force causes an object to move in the direction of the force. • Work Equation work = force displacement (Change in position) W = F x ( x)

• Work is measured in joules (J). • 1 joule is roughly equal to the energy required to lift a small apple 1 meter – 1 J = 1 N • m = 1 kg • m 2/s 2 • Power is the rate at which work is done or energy is converted. James Prescott Joule – power = work / time (P=W/t) – Measured in watts (W) – 746 watts = 1 horsepower

Work & Energy • Energy is the ABILITY to do work. • When you do work on an object, you transfer energy to that object. • Whenever work is done, energy is transformed or transferred to another system. • Energy is also measured in joules. • Energy is not a substance!

Energy Systems • Scientist study energy systems. • Boundaries define a system and are set by the observer. • Systems may be open or closed. • When the flow of energy into and out of a system is small enough that it can be ignored, the system is called a closed system. • Most systems are open systems, which exchange energy with the space that surrounds them.

Kinetic Energy • Kinetic Energy (KE or Ek) – Energy of a moving object due to the object’s motion. • Kinetic energy depends on… – Mass: more mass = more KE – Speed: faster = more KE • Kinetic Energy Equation Ek = ½ mv 2

Potential Energy • Potential Energy – Energy that an object has because of the position, shape, or condition. • Potential energy is stored energy. • There are many types of potential energy that we will cover… • • • Gravitational Elastic Chemical Electrical Magnetic • Potential Energy + Kinetic Energy = Mechanical Energy

Gravitational Potential Energy • Gravitational potential energy (GPE or Eg) depends on: – Mass: more mass = more GPE – Height: higher = more GPE – Acceleration due to Earth’s gravity: 9. 8 m/s 2 (same everywhere on Earth) – The state test may use 10 m/s 2 • Gravitational Potential Energy Equation GPE (Eg)= mass (m) acceleration due to Earth’s Gravity (g) height (h) GPE (Eg) = mgh • The height can be relative.

Law of Conservation of Energy • Law of Conservation of Energy – States that energy cannot be created or destroyed. • Energy doesn’t appear out of nowhere. • Whenever the total energy in a system increases, it must be due to energy that enters the system from an external source. • Energy is transformed to another type or transferred to another system/object. – Energy doesn’t disappear, but it can be changed to another form.

Conservation of Energy • Kinetic Energy (Ek) • Gravitational Potential Energy (Eg) • Kinetic Energy + Potential Energy = Mechanical Energy

Exit Ticket #5 – Work and Energy • Questions 37 - 40

Question #37 • Work is: A. The force exerted on a body through a change in position (displacement) B. Mass times acceleration C. Distance traveled divided by the time. D. Force divided by acceleration

Question #38 The units of work are: A. B. C. D. Newtons Watts Joules Horse power

Question #39 What is the gravitational potential energy (Eg) of a 1 kg box that is 10 m above the ground? (g = 9. 8 m/s 2) a. 9. 8 J b. 980 J c. 9800 J d. 98 J

Question #40 This is a measure of the ability to do work: A. Force B. Acceleration C. Velocity D. Energy