Energy What is it?

Here are some examples: Here are some examples:

Definition Energy is the ability to cause change Energy is the ability to cause change Two types of energyTwo types of energy Kinetic Kinetic Potential Potential

Kinetic Energy in the form of motion Energy in the form of motion RunningRunning ThrowingThrowing FlyingFlying How much kinetic energy depends on what? How much kinetic energy depends on what? Mass and VelocityMass and Velocity Question: What has more kinetic energy: a truck traveling at 100 km/hr or a motorcycle traveling at 100 km/hrQuestion: What has more kinetic energy: a truck traveling at 100 km/hr or a motorcycle traveling at 100 km/hr How about a truck traveling at 100 km/hr or a truck traveling at 80 km/hrHow about a truck traveling at 100 km/hr or a truck traveling at 80 km/hr

Potential Energy Stored Energy Stored Energy Students sitting in their seatsStudents sitting in their seats A bullet in a gunA bullet in a gun BatteryBattery Potential energy changes into kinetic energy Potential energy changes into kinetic energy

Work Transfer of energy through motion Transfer of energy through motion In order for work to take place, a force must be exerted through distanceIn order for work to take place, a force must be exerted through distance Calculating Work:Calculating Work: Work = Force x Distance Work = Force x Distanceor W = F x D W = F x D

Units Work is expressed in Newton-meters Work is expressed in Newton-meters (N x m) Or Joules (j) Named after British Scientist James Prescott Joule Named after British Scientist James Prescott Joule

Example A student’s full backpack weighs 30 N. She lifts it from the floor to a shelf 1.5 m high. How much work is done on the pack full of books? A student’s full backpack weighs 30 N. She lifts it from the floor to a shelf 1.5 m high. How much work is done on the pack full of books? W = F x D W = F x D F= 30 N F= 30 N D = 1.5 m D = 1.5 m W = ? W = ? W= 30N x 1.5 m W= 30N x 1.5 m W = 45 N x m or 45 J W = 45 N x m or 45 J

Try This One A carpenter lifts a 4.5 kg beam 1.2 meters. How much work is done on the beam? A carpenter lifts a 4.5 kg beam 1.2 meters. How much work is done on the beam? What do you know?What do you know? Distance = 1.2 m Distance = 1.2 m Force = ? You must calculate force Force = ? You must calculate force F = M x AM = 4.5 kg A = ?F = M x AM = 4.5 kg A = ? A = gravity = 9.8 m/s 2A = gravity = 9.8 m/s 2 F = 4.5 kg x 9.8 m/s 2 F = 44.1 NF = 4.5 kg x 9.8 m/s 2 F = 44.1 N W = 44.1N x 1.2 m W = J W = 44.1N x 1.2 m W = J

Another Example A man pushes a lawnmower with a force of 500 N for 200 m. How much work is this if the force of friction acting on the lawnmower is 150 N? A man pushes a lawnmower with a force of 500 N for 200 m. How much work is this if the force of friction acting on the lawnmower is 150 N? W = F x DW = F x D F = 500 N N F = 500 N N D = 200 m D = 200 m W = 650 N X 200 mW = 650 N X 200 m W = JoulesW = Joules

One more example Cheerleader A is holding up cheerleader B. Cheerleader B is exerting a force a 80 N on cheerleader A. If cheerleader A walks forward 2 meters while holding cheerleader B, how much work has cheerleader A done? Cheerleader A is holding up cheerleader B. Cheerleader B is exerting a force a 80 N on cheerleader A. If cheerleader A walks forward 2 meters while holding cheerleader B, how much work has cheerleader A done? No work!!!! Why? No work!!!! Why? Because work was not done over a distance Because work was not done over a distance W = F x D W = F x D W = 80 N x 0 m W = 80 N x 0 m W = 0 N x m or 0 Joules W = 0 N x m or 0 Joules