Forces/Energy Chapter 4 Notes
● Work is the transfer of energy. The ability to do work or cause change is called energy. Both are measured in a unit called Joules. ● Power is the rate at which energy is transferred. To understand the amount of power needed, you would divide transferred energy (work) by unit of time. ● The two basic kinds of energy are: kinetic energy and potential energy. ● Whether energy is potential or kinetic depends on the motion, position, and shape of the object. ● The energy an object has due to its motion is called kinetic energy. ● Kinetic energy depends on the speed and mass of an object; the energy increases as mass and speed increase. Objects will have greater kinetic energy will have more speed because in the equation to find kinetic energy speed is doubled. ● To calculate kinetic energy, you must know the equation. ○ Kinetic energy = ½ x mass x speed^2 ○ Example: What would the kinetic energy of the girl be if her mass is 10 kg and her speed is 3m/s. Her Kinetic Energy would be 30 J. Know how to solve kinetic energy.
● Objects do not have to be moving to have energy, some objects have energy as a result of their shapes or positions. Objects that have potential energy have the potential to do work. ● Gravitational potential energy of an object is equal to its weight multiplied by its height. ● Elastic potential energy is the energy associated with objects that can be compressed or stretched. An object has a different type of potential energy due to its shape. ● The SI unit for each quantity is: ○ Force - Newtons ○ Height - Meters ○ Work - Joules ○ Mass - Kilograms ○ Energy - Joules
● The form of energy associated with the motion, position and shape of an object is called mechanical energy. An object’s mechanical energy is a combination of its potential energy and kinetic energy. ● To find the amount of mechanical energy an object has you would add its potential energy to its kinetic energy. (potential energy + kinetic energy = mechanical energy. An object with mechanical energy can do work on another object. ● Forms of energy associated with the particles of objects include: nuclear energy, chemical energy, thermal energy, electrical energy and electromagnetic energy. ○ Nuclear energy is a type of potential energy that is stored in the nucleus of an atom. Nuclear energy is released during a nuclear reaction: nuclear fission or nuclear fusion. Both types of reactions release stored energy in the nuclei of atoms. A nuclear fission reaction releases energy when a nucleus splits apart, and a nuclear fusion releases energy when nuclei join together. ○ Thermal energy is the total amount of kinetic and potential energy of the particles in an object. The more kinetic energy the particles in an object have the greater the thermal energy. For example: while boiling a pot of water, as the bubbles move fast, the temperature of the water increases. ○ Electrical energy can either be kinetic or potential depending on whether the electrical charges are moving or stored. Lightning and batteries are forms of electrical energy. ○ Electromagnetic energy is a form of energy that travels through space in waves. These waves do not require a medium, so they can travel through a vacuum or empty space. Cell phones send and receive messages using microwaves. ○ Chemical energy is the potential energy stored in chemical bonds. Chemical energy is in the foods we eat; our body stores the energy in our bodies as bonds. Bonds are broken in your cells that release energy for your body to use.
● All forms of energy can be transformed into other forms of energy. A change from one form to another is called energy transformation. ○ Single transformations happen when one form of energy needs to be transferred into another to get work done. Example: A toaster transforms electrical energy to thermal energy to toast your bread/waffle. ○ Multiple transformations happen when a series of energy transformations is needed to do work. Example: The mechanical energy used to strike a match is transformed first to thermal energy. The thermal energy causes particles in the match to release stored chemical energy, which is then transferred back to thermal energy and to the electromagnetic energy as the light.
● The law of conservation of energy states that when one form of energy is transformed to another, no energy is created or destroyed. The total amount of energy is the same before and after the transformation. ● Friction transforms mechanical energy to thermal energy. Example: when your hands are cold and you rub them together, your hands will warm up which is a result of friction converting that mechanical energy of your moving hands to thermal energy.