Chapter 5 Energy

5.1 What is Energy? Energy: the ability to do work or cause change Work: Force * Distance Work is done if a force makes something move. In other words, when work is done, a change occurs. When work is done and change occurs, energy moves from one place to another or changes form.

Two Types of Energy All forms of energy fall into two types: kinetic and potential. Potential energy: energy that is stored; also energy that is due to position Kinetic energy: energy that is in motion; also depends on the mass and speed of an object

Energy Analogy Money can be stored and converted into a variety of forms, like: Cash (bills and coins), check, credit card, bank account. Energy can also be stored and converted into different forms Different energies are just different forms of the same thing: ENERGY

Converting Kinetic and Potential Energies One energy form can transfer into other energy forms. Example: a swinging pendulum (shown on next page)

Potential Energies There are many types of potential energies: Chemical Nuclear Elastic Gravitational

Potential: Chemical Energy Chemical Energy: energy stored in the bonds of atoms and molecules. Examples: food, coal, natural gas, and paper all contain chemical energy. Calorie: food energy / 1g (fat=9C, carbs/protein=4C)

Potential: Nuclear Energy Nuclear energy: energy stored in the nucleus of an atom. Examples: Stars, uranium (power plants), plutonium (weapons). Mass transfers into energy with fusion!

Potential: Elastic Energy Elastic Energy: energy stored in objects that can be compressed or stretched Examples: stretched rubber band, a compressed spring

Potential: Gravitational Energy Gravitational Energy: the energy stored in objects due to mass & position above Earth. Examples: water on top of a waterfall, airplane GPE is calculated by the equation: GPE= mGh=mass kg*acceleration Gravity*height m Unit for GPE is Joules! Acceleration due to gravity = G = 9.8m/s2

GPE Example 1 GPE: Mass * 9.8 m/s2 * Height A 250 kg boulder is sitting on the edge of a cliff that is 60m high. GPE=mGh GPE = 60m * 9.8m/s/s * 250kg GPE = 147000 Joules

GPE Example 2 GPE: Mass * 9.8 m/s2 * Height A 10 kg brick is sitting on a platform that is 15 meters high. GPE? GPE = 10kg * 9.8m/s/s * 15m GPE = 1470 Joules

GPE Example 3 GPE: Mass * 9.8 m/s2 * Height An 8 kg binder is sitting on a desk that is 1.5 meters high. GPE? GPE = 8kg * 9.8m/s/s * 1.5m GPE = 117.6 Joules

Kinetic Energies Kinetic energy is the energy of motion. It can be calculated with the equation: ½ * mass * (velocity)2 There are many types of kinetic energies: Radiant Thermal Electrical Mechanical Sound

Kinetic Energy Calculation Equation: KE = ½ * mass * (velocity)2 A car whose mass is 1000 kg moves at a speed of 20 m/s. Find the kinetic energy KE = ½ (1000kg) x (20m/s) x (20m/s) KE = ½ (1000) (400) = 200,000 J

Kinetic: Radiant Energy Radiant energy: the energy that travels in electromagnetic waves. Examples: radio wave, microwave, infrared, visible light, ultraviolet light, x-ray, gamma ray This is sometimes referred to as electromagnetic energy.

Kinetic: Thermal Energy Thermal Energy: energy caused by the internal vibration of atoms or molecules. Examples: fire, or a warm slice of pizza

Kinetic: Electrical Energy Electrical Energy: energy from the movement of electrons. Examples: lightning, electricity

Kinetic: Mechanical Energy Mechanical energy: energy occurring when an object is in motion. Mechanical energy is also the sum of kinetic and potential energies. Examples: moving water, biking

5.1 NRG Analysis: Date___ Name_____________Hr__ Copy / answer in sentences. Show all work. Explain if objects can have kinetic and potential energies at the same time. Explain how kinetic energy of trucks can increase without changing their speed. Find KE: mass=0.06kg, v=50m/s Find GPE: mass=80kg, h=5m

Law of Conservation of Energy Law of Conservation of Energy: states that energy cannot be created or destroyed; it transfers from one form to another. The total amount of energy in the universe does not change.

Energy Conversions Energy transfers from one form to another. Most energy in the universe is converted into thermal energy due to friction. Examples: Your body will convert chemical energy from food into what other types? Using a blow dryer will convert electrical energy into what other types?

Explain the NRG Conversion Energy begins in the sun as NUCLEAR. Nuclear energy transfers into THERMAL and RADIANT.

NRG Conversion Continued Radiant energy enters Earth’s atmosphere. Plants store radiant energy into CHEMICAL ENERGY.

NRG Conversion Continued Coal, a non-renewable energy source, provides 45% of the electrical energy in the U.S. What other forms of energy could we use to produce electrical energy?

Explain the Conversions

5.2 Law Analysis: Date___ Name_____________Hr__ Copy / answer in sentences. Show all work How does friction affect mechanical NRG? Explain which has more potential energy, a car on a mountain or on a hill. A swing PE is 200J at its highest point & 50J at lowest. What is KE at lowest point?