Chapter 4 Energy

4-1: The Nature of Energy When something is able to change its environment or itself, it has energy.

Energy energy – the ability to cause change or the ability to do work Types of Energy kinetic energy – energy in the form of motion – the amount of kinetic energy that an object has depends on its mass and velocity – the greater the mass and the greater the velocity the more its energy – kinetic energy is measure in Joule (J)

Kinetic Energy

Energy energy – the ability to cause change or the ability to do work – equation: m = mass & v = velocity

Energy If a truck is moving at a velocity of 30 m/s and has a mass of 500 kg, what is its kinetic energy?

Energy energy – the ability to cause change or the ability to do work Types of Energy potential energy – energy that is stored and based on an objects position – potential energy can be converted to kinetic energy when something acts to release it example: a book sitting on a shelf has potential energy but when it falls that potential energy is converted into kinetic energy

Energy Potential vs. Kinetic Energy

Energy potential energy – energy that is stored and based on an objects position Types of Potential Energy – elastic potential energy is stored by something that can stretch or compress examples: rubber band, spring, or shocks

Energy potential energy – energy that is stored and based on an objects position Types of Potential Energy – chemical potential energy is energy that is stored in chemical bonds examples: food that we eat, gasoline

Energy potential energy – energy that is stored and based on an objects position Types of Potential Energy – gravitational potential energy (GPE) is energy that is stored by objects that are above the Earth’s surface examples: an apple falling from a tree, a skydiver jumping out of an airplane

Energy gravitational potential energy (GPE) is energy that is stored by objects that are above the Earth’s surface – m = mass (kg) – g = acceleration due to gravity (9.8 m/s 2 ) – h = height (m)

Energy A 2 kg ball is dropped on Mr. Thomsen’s head from a height of 10 m. Before it was dropped, how much gravitational potential energy did the ball have?

Energy Relationship Between Kinetic & Potential Energy – As an object drops, potential energy decreases but kinetic energy increases – Since an object is moving while it is dropping, it is gaining kinetic energy – Since an object is no longer at a higher elevation, it is losing potential energy

Energy Potential vs. Kinetic Energy

Conservation of Energy Energy is constantly being transformed from one form to another. For example, a light bulb is transforming electrical energy into light energy, or a car engine transforms chemical energy stored in gasoline into kinetic energy.

Conservation of Energy mechanical energy – the total amount of potential and kinetic energy in a system Mechanical Energy = Potential Energy + Kinetic Energy – involves both position and motion of an object – the total mechanical energy stays constant while an object falls because potential energy decreases but kinetic energy increases

Conservation of Energy Mechanical Energy

Conservation of Energy Law of Conservation of Energy – energy cannot be created or destroyed only transferred from one form to another – this law implies that the amount of energy in the universe remains constant

Conservation of Energy Law of Conservation of Energy – energy cannot be created or destroyed only transferred from one form to another – example: If you are on a swing and stop pumping your legs, you will eventually come to a stop. So, the swing will then have NO kinetic energy. Where does the energy go? The swing’s ropes rub on their hooks and some of the energy turns into thermal energy (heat). Air resistance can cause an increase in air temperature.

Conservation of Energy Law of Conservation of Energy – energy cannot be created or destroyed only transferred from one form to another – The swing’s ropes rub on their hooks and some of the energy turns into thermal energy (heat). Air resistance can cause an increase in air temperature. – Energy Lost = Energy Gained