Work, Power, and Energy

Work, Power, and Energy


Work is when force is applied to an object. Work = Force X Distance Force is measured in Newtons (N) Distance is measured in Meters (m) (W = FD) Work is zero when an object is not moving. Work is measured in Joules (J). 1 Joule = 1 Newton X 1 Meter J = Nm WORK EXAMPLE Imagine a father playing with his daughter by

lifting her repeatedly in the air. How much work does he do with each lift if he lifts her 2.0 m and exerts an average force of 190 N? Given: F = 190 N, d = 2.0 m Unknown: W = ? (J) Remember: work = force X distance W= 190 N X 2.0 m = 380 Nm = 380 J WHAT IS POWER? Power is the rate at which work is done or how much work is done in a given time. Power = Work P= W

Time t Power is measured in Watts (W) POWER EXAMPLE Dante uses 14 J of work to lift a weight for 20 seconds. How much power did he use? Given: Work= 14 J, Time = 20 seconds Unknown: Power (W) Remember: Power = Work P= W

Time t Power = 14 J / 20 s = 0.7 W WHAT IS ENERGY? Energy is the ability to do work. Energy is associated with moving objects. Whenever work is done, energy is transformed or transferred. Energy is measured in Joules (J). There are two main types of energy: 1. Kinetic Energy- energy of an object in motion

2. Potential Energy- energy an object has due to its position or shape, stored energy THE LAW OF CONSERVATION OF ENERGY Energy is not created nor destroyed! It can only transformed be transformed into different types of energy! TYPES OF ENERGY Forms of Potential Energy Forms of Kinetic Energy

Gravitational- energy of position or place Electrical- movement of electrical charges Chemical- energy stored in the bonds of atoms and molecules Radiant- light or solar energy Stored Mechanical- energy stored

in objects by the application of a force Thermal- heat energy Nuclear- energy stored in the nucleus of an atom, the energy that holds the nucleus together Motion- movement of objects and substances from one place to another Sound- vibration energy

POTENTIAL ENERGY Potential energy is energy stored by an object. Potential energy is energy waiting to do something. Potential energy changes into kinetic energy when motion occurs. Type of potential energy is Gravitational (GPE) GPE depends on the mass and height of an object. Increase in height, increases the GPE. Increase in mass, increases the GPE. GPE = Mass X Gravity X Height

GPE = mgh POTENTIAL ENERGY EXAMPLE A 65 kg rock climber ascends a cliff. What is the climbers gravitational potential energy (GPE) at a point 35 m above the base of the cliff? Given: mass = 65kg, height = 35m, gravity = 9.8 m/s2 Unknown: GPE (J) Remember: GPE = Mass X Gravity X Height GPE = (65kg)(9.8m/s2)(35m) GPE = 2.2 X 104 J

KINETIC ENERGY Kinetic energy is the energy of an object due to the objects motion. It depends on the objects mass and rate of acceleration. Speed = distance over time (d/t) Kinetic Energy= X mass X speed squared KE = mv2 KINETIC ENERGY EXAMPLE What is the Kinetic Energy of a 44 kg cheetah running at 31 meters per second? Given: mass= 44 kg, speed= 31 m/s

Unknown: Kinetic Energy (J) Remember: Kinetic Energy= X mass X speed squared KE = mv2 KE= (44kg)(31 m/s)2 = 21.104 J

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