Presentation on theme: "Energy and Conservation Physics Chapter 5-2 (p172-178) Chapter 5-3 (p179-183)"— Presentation transcript:
Energy and Conservation Physics Chapter 5-2 (p172-178) Chapter 5-3 (p179-183)
Types of Energy -Energy is measured in Joules - Kinetic energy (KE) – energy of a moving object due to its motion KE = ½ mv 2 KE kinetic energy (J) m mass (kg) v velocity (m/s)
- KE depends on speed (velocity) and mass More speed (velocity) or more mass = higher KE - BUT velocity is more important
- Potential energy (PE) – stored energy; energy of position 2 kinds of potential energy
Types of Potential Energy 1. Gravitational (PEg) Associated with an objects’ position / height PE g = mgh (do not use negative sign with gravity here) m = mass (kg) g = magnitude of gravity (m/s 2 ) h = height above the ground (m)
The higher the object above the ground, the more gravitational potential energy the object has.
Types of Potential Energy 2. Elastic Potential Energy (PE e ) energy in a stretched or compressed spring PE elastic = ½ kx 2 k = spring constant (N/m) x = distance compressed or stretched (m)
- Spring constant – (force constant) – the measure of a spring’s resistance to being stretched or compressed measured in N/m
Work and Energy ǽ⅞. Other forms of energy 1. Kinetic molecular energy energy of moving atoms and molecules 2. Chemical energy energy released in chemical reactions energy stored in the food you eat
Work and Energy 3. Nuclear energy nuclear reactions (fission, fusion), the sun 4. Solar energy sunlight, electromagnetic waves 5. Electrical energy electricity, movement of charged ions and electrons
Conservation of Energy A. The Law of Conservation of Energy – Energy cannot be created or destroyed, but can only change form. 1. Potential energy changes to Kinetic energy as a ball rolls down a hill (stored energy changing slowly to energy of motion.) 2. This transformation occurs slowly, NOT all at once. 3. At the top of the hill all the energy is potential, at the bottom of the hill all the energy is kinetic (until the ball stops rolling) 4. Some energy is lost to friction and heat, but it is not destroyed
-Mechanical Energy – the sum of all kinetic energy and all forms of potential energy ME = KE + ΣPE ΣPE = ΣPEg + ΣPEe - In the presence of friction ME is not conserved, because some of the energy is lost to friction, and changes into other forms of energy, such as light, and heat ***The total energy of a system is always conserved!!