Energy
The Unit for all types of Energy: Joule (J) James Prescott Joule His Experiment linking potential, kinetic and thermal energy
(energy of motion and position) Mechanical Energy (energy of motion and position) Gravitational Potential Energy Elastic Potential Energy Kinetic Energy An object can have more than one type of energy Slide 10-10
The energy of an object from its motion. Kinetic Energy The energy of an object from its motion.
Example Problem #1: A 10 kg bowling ball moves at 3.0 m/s. What is the bowling ball’s kinetic energy?
Example Problem #2 A 10 kg bowling ball moves at 3.0 m/s. How fast would a 10 g bullet have to travel in order to have the same kinetic energy as the bowling ball?
Gravitational Potential Energy The energy of an object due to its elevation above the ground g = 9.8 m/s2 Note: g is positive here!
Example Problem #3: A 10 kg bowling ball is held 1.8 m above the ground. Calculate the potential energy of the bowling ball.
Kinematics and Energy What patterns did you notice in the energy of the falling apple?
Law of Conservation of Energy The Total Energy of a system remains constant.
Law of Conservation of Energy
Thermal Energy (TE) Energy due to the motion of the molecules Friction and Air Resistance convert kinetic energy to thermal
Law of Conservation of Energy Mechanical Energy
Work Work: transfer of energy to or from an object by the application of a force
Work Equation Unit for Work: Joule (J) Angle between the Force and Distance Unit for Work: Joule (J)
Work Example You pull a 20 kg box with a force of 50 N for 1.5 meters. How much work do you do if you pull at an angle of 30°? b) How much work do you do if you pull horizontally?
Sign of Work The sign of work is important: Positive Work (adds energy – speed up object) Negative Work (removes energy) (slow down object)
Which force is doing work? Positive or Negative work? A textbook slides to a stop along the table: An apple falls from a tree: A box is pushed across a carpet:
Work Kinetic Energy Theorem The net work (Wnet) performed on the object can cause a change in kinetic energy (ΔKE)
Work Kinetic Energy Theorem 2. A car that has a mass of 2000 kg is traveling down the highway at 30 m/s and speeds up to a speed of 35 m/s over the course of 54 m. What force is needed from the car’s engine?
Work -Potential Energy Theorem The net work (Wnet) performed on the object can cause a change in potential energy (ΔGPE)
Work-Potential Energy Theorem 3. How much work is performed by a person in lifting a 1 kg book from a table 0.25 m high and placing it on a shelf 2.0 m high?
Power Rate at which work is done Same Work Different Power VS. Running vs. walking up a flight of steps Same Work Different Power
Power Rate at which work is done or rate at which energy is transferred Eqn: Units:
Power 4. At what rate is a 60 kg boy using energy when he runs up a flight of stairs 3 m high in 8 seconds?