I. Energy. The ability of an object to produce a change. Energy is measured in Joules. In this unit we cover 3 types of energy: 1. Potential (stored) energy 2. Kinetic (motion) energy 3. Thermal (heat) energy. Types of KE and PE. Potential Energy Kinetic Energy
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1. Potential (stored) energy
2. Kinetic (motion) energy
3. Thermal (heat) energy
1. This is why work and energy are both measured in Joules 1 J = 1 kgm2 / s2
1. Calorie (1 cal = 4.184 J)
2. British Thermal Unit (1 BTU = 1055 J)
1. Gravitational Potential Energy.
ex. Anytime an object has height.
2. Elastic/Spring Potential Energy.
ex. Rubber band, bouncy ball
3. Chemical Potential Energy.
ex. Bonds in food and gasoline
1. You must set a zero height that we call our reference level.
1. Ex: rubber band, Trampoline
1. Ex: gasoline, food
1. Ex: static electricity, magnets
Use this principle to determine the blanks in the following diagram. Knowing that the potential energy at the top of the tall platform is 50 J, what is the potential energy at the other positions shown on the stair steps and the incline?
1. What is the gravitational potential energy relative to the floor? (41.2 J)
2. What is the gravitational potential energy relative to the head of a 1.65 m tall person? (8.8 J) (hint, the person’s head is now the reference point).
If the work done is negative, the object loses energy.
p. 259: Work is the transfer of energy by mechanical means.
A ball thrown into the air has energy that changes from kinetic to potential at the top and then back to kinetic at the bottom.
1. What is the child\'s gravitational potential energy at the top of the swing? (274.4 J)
2. What is the child’s velocity at the bottom of the swing? (4.0 m/s)
1. The objects bounce off each other.
a. Example: Billiard balls
1. Ex. A compressed spring is released during a collision
1. The particles are held together by electromagnetic forces (strongest in solids, weakest in gases) (states of matter)
In a hot object, the particles move faster, therefore they have more kinetic energy. (expand with more thermal energy - thermal expansion)XIV. Kinetic-Molecular Theory
1. Thermal energy is measured in joules.
1. Temperature shows a direct relationship with the average kinetic energy of the particles in an object.
1. Heat is measured in Joules.
A. Conduction – the transfer of thermal energy when particles collide
1. Ex: a metal spoon gets hot when sitting in boiling water.
B. Convection – the rising of hot air/liquids pushing cooler air/liquids down.
1. Ex: thunderclouds
C. Radiation – the transfer of energy by electromagnetic waves
1. Ex: sunlight heating the Earth
A. A heat engine is a machine that is able to convert thermal energy to mechanical energy.
1. The total increase in the thermal energy of a system is the sum of the work done on it and the heat added to it.
2. Only restates the law of conservation of energy.
1. Natural processes go in a direction that increase the total entropy of the universe.
2. Entropy is the measure of disorder in an object