Mechanical energy

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Objectives : 

Objectives Define energy & name the unit of measurement Define mechanical energy Calculate potential and kinetic energy State the law of conservation of energy

What is Energy? : 

What is Energy? Energy is the ability to do work This is similar to our every day definition of energy. You can’t run up the stairs (work) without energy! We have lots of types of energy. Can you name a few?

Forms of Energy : 

Forms of Energy

Mechanical Energy : 

Potential energy + Kinetic energy = Mechanical energy Mechanical Energy Potential energy is stored energy or energy of position Kinetic energy is the energy of motion

Kinetic Energy : 

KE = mv2 / 2 M = mass of the object (kg) V = velocity of the object (m/s) Measured in Joules Kinetic Energy

Let’s Practice : 

Let’s Practice What is the kinetic energy of this car when it is traveling 38.0 m/s? KE = m v2 / 2 = (1550 kg)(38.0 m/s)2 / 2 KE = 1,119,100 J Car’s mass = 1550 kg

Potential Energy : 

PE = mgh   m = mass (kg) g = gravitational acceleration due to gravity (9.8 m/s2) h = height above earth's surface (m) Measured in Joules Potential Energy

Let’s Practice : 

Let’s Practice A rock has a mass of 840 kg. The center of mass is 29.0 m above the ground. How much energy does it have? PE = mgh m = 840 kg g = 9.8 m/s2 h = 29.0 m PE = (840 kg)(9.8 m/s2)(29 m) = 238,728 J

Energy Conversion : 

Energy Conversion Energy can be changed from one form to another. Changes in the form of energy are called energy conversions.

Conservation of Energy : 

Conservation of Energy Energy can change from one form to another, but the total amount of energy is always the same.

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