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Energy of Motion. What is Energy?. Definition: Energy is the ability to do work. Work is done when a force moves an object over a given distance. Engineering Connection:. Engineers need to understand the many different forms of energy in order to design useful products
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What is Energy? Definition: Energy is the ability to do work. Work is done when a force moves an object over a given distance.
Engineering Connection: Engineers need to understand the many different forms of energy in order to design useful products • Mechanical engineers are concerned about the mechanics of energy — how it is generated, stored and moved. • Product design engineers apply the principles of potential and kinetic energy when they design consumer products. For example, a pencil sharpener employs mechanical energy and electrical energy. • When designing a roller coaster, mechanical and civil engineers ensure that there is sufficient potential energy (which is converted to kinetic energy) to move the cars through the entire roller coaster ride.
Introduction • All energy is classified into two broad categories: Potential Energy & Kinetic Energy • Either form of energy can change into the other. You need energy in order to get things done. For example, you know that your body must use energy if you want to pick up a box and move it across the room.
Potential Energy Potential energy is energy an object has because of its position 0r composition. Potential energy is stored energy. It has the “potential” to do work.
Potential Energy -example • A rock at the edge of a cliff has potential energy due to its position. Gravitational force can pull the rock down to the bottom of the cliff.
Potential Energy -example • Fuel, such as gasoline or coal, also has potential energy. When the fuel burns, the energy stored in its chemical bonds is released.
Calculating Potential Energy Potential energy is measured in Joules (J). • Near Earth, you can calculate an object’s gravitational potential energy (PE) by the following formula: GPE = mass x g x height GPE is the gravitational potential energy mass is the mass in kilograms height is the height in meters g is the acceleration due to gravity At sea level, g = 9.8 meters/sec2or 32.2 feet/sec2. .
Calculating GPE - example • Suppose a rock at the edge of a cliff has a mass of 10 kg, and its height above the ground below is 100 m. • GPE = mgh =10 kg x 9.8meters/sec2 x 100 m = 9800 J
Kinetic Energy • Definition: The energy of motion Kinetic energy is the energy an object has because of its motion and is also measured in Joules (J). Any object that is moving has kinetic energy
Kinetic Energy- Example • An example is a baseball that has been thrown. The kinetic energy depends on both mass and velocity
Calculating Kinetic Energy • Kinetic Energy can be expressed mathematically as follows: • KE stands for kinetic energy. • Mass is in kilograms • V is the speed in meters per second Note that a change in the velocity will have a much greater effect on the amount of kinetic energy because that term is squared. :
Calculating Kinetic Energy • The 1 kg ball is moving at a speed of 20 m/s. • KE = ½ mv2 = 0.5 x 1 kg x (2o m/s)2 = 0.5 x 1 x 400 = 200J
Potential and Kinetic Energy Transformations • Potential energy can change into kinetic energy, and vice versa.
Mechanical Energy • The total amount of mechanical energy in a system is the sum of both potential and kinetic energy, also measured in Joules (J). Total Mechanical Energy = Potential Energy + Kinetic Energy
Total Mechanical Energy = Potential Energy + Kinetic Energy
Conservation of Energy • energy can change from one form into another. • Due to the principle of conservation of energy, energy can change its form (potential, kinetic, heat/thermal, electrical, light, sound, etc.) but it is never created or destroyed.
Law of Conservation of Energy • In the perfect physics world, a pendulum will swing forever. Energy is constantly transferred between potential and kinetic energies.
Law of Conservation of Energy • In the real world, a swinging pendulum eventually stops due to friction. However, the total energy of the pendulum never changes. The energy is transferred from potential energy to kinetic energy. The friction is shown as a form of heat energy which includes air resistance and sound energy.
Potential and Kinetic Energy Transformations • Potential energy can change into kinetic energy, and vice versa. In the perfect physics world, a person can jump from a diving board and hit the water with the same amount of energy as they had before they jumped. Energy is transferred from potential energy to kinetic energy until they hit the water. When the diver hits the water, kinetic energy is transferred into heat and sound energies. The energy of the system is transferred from potential to kinetic to heat.
Conservation of Energy • energy can change from one form into another. • Due to the principle of conservation of energy, energy can change its form (potential, kinetic, heat/thermal, electrical, light, sound, etc.) but it is never created or destroyed.
