Unit 2: Energy THERMAL ENERGY HEAT TRANSFER POTENTIAL VS. KINETIC ENERGY WORK POWER SIMPLE MACHINES

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1 Unit 2: Energy THERMAL ENERGY HEAT TRANSFER POTENTIAL VS. KINETIC ENERGY WORK POWER SIMPLE MACHINES

2 Bellringer Day What is energy? 2. There are different forms of energy. Name two.

3 What is Energy? Energy is the ability to do work-in other words, to cause change In order for something to change, there must be a transfer of energy from one thing to another This unit we will be discussing energy in its different forms, including thermal, potential/kinetic, and the ability to do work.

4 What Energy Is And Is NOT Energy is not a substance It cannot be weighed It does not take up space Energy is a condition! The Law of Conservation of Energy says: Energy cannot be created or destroyed. It can only be transformed from one type to another or passed from one object to another.

5 Thermal Energy HEAT AND TEMPERATURE

6 What is Thermal Energy? Thermal Energy is the energy that comes from heat Heat is generated by the movement of tiny particles within an object The faster these particles move, the more heat is generated We measure heat by recording the temperature of something

7 Thermal Energy and Particles When the motion of particles in an object increases, so does the temperature When the motion of particles in an object decreases, so does the temperature

8 Measuring Thermal Energy Temperature indicates the average speed of particle motion in a substance The Celsius Scale is the common scientific measurement of temperature using the unit degrees; based on the freezing and boiling points of water Water boils at a temperature of 100 o Celsius and freezes at 0 o Celsius Other degrees of temperature include Fahrenheit and Kelvin

Absorbing and Releasing Thermal Energy Depending on the material, heat may be absorbed or released Insulation is the process of trapping thermal energy to keep warm Objects

9 Absorbing and Releasing Thermal Energy Depending on the material, heat may be absorbed or released Insulation is the process of trapping thermal energy to keep warm Objects releasing heat energy will be getting colder, and objects absorbing heat energy will be getting warmer Keep in Mind: Thermal energy always travels from the warmer object to the cooler object

Thermal Energy Absorption Experiment Four

The dull black container would be the warmest

10 Thermal Energy Absorption Experiment Four containers were placed equidistant from a heater. Which container would have the warmest water after ten minutes? Shiny Metal Dull Metal Shiny Black Dull Black The dull black container would be the warmest after 10 minutes. It is an insulator, and good at absorbing heat. The shiny metal would be the coolest. It s surface is reflecting heat.

11 Bellringer Day What is the difference between heat and temperature? 2. If you zoomed in on the molecules of a hot object vs. a cold object, what difference would you see? 3. Name one way that homes are designed to insulate heat energy.

12 Heat Transfer CONVECTION, CONDUCTION, AND RADIATION

13 Heat Transfer Thermal energy always flows from warm to cool Hot objects in a cooler room will cool to room temperature Cold objects in a warmer room will heat up to room temperature

14 Methods of Heat Transfer Heat transfers from one object to another in three ways: Conduction Convection Radiation

15 Conduction Heat energy travels when two objects at a different temperature are in direct contact with each other (touch) During heat conduction, vibrating atoms/molecules excite the atoms/molecules next to them.

16 Case Study: Why does metal feel colder than wood, if they are both at the same temperature? Metal is a conductor, wood is an insulator. The metal feels colder because it is a better conductor-heat moves easily out of your warmer hand into the colder metal The wood feels warmer because it is a poor conductor. Little heat moves out of your hand into the wood, so your hand does not sense that it is touching something cooler

17 Convection The transfer of heat through a fluid, such as liquid or gas The hot, less dense fluid rises while cold, more dense fluid sinks, resulting in the transfer of heat

18 Case Study: Convection in a Refridgerator Freezers are generally located on the top of the fridge. This creates a convection system, where the cold air from the freezer sinks and cools the lower units

19 Radiation Heat energy travels as electromagnetic waves from the sun

20 Bellringer Day If a cup of hot coffee and a red popsicle were left on the table in this room what would happen to them? Why? 2. Create a chart comparing the three methods of heat transfer.

21 Thermal Energy PHASE CHANGES

22 Heat Recall that heat is the thermal energy that is transferred from particles at a higher temperature to particles at a lower temperature

23 Phase Changes A phase change diagram shows the relationship of the particles in matter as heat energy is transferred Notices as particles heat up and temperature increases, they change phase (Ice Water Water Vapor)

24 Specific Heat Specific Heat is the amount of heat energy required to raise 1 g of the material 1 C Water has a high specific heat, meaning it takes a lot of energy to raise the temperature of water Thermal energy is determined through the formula Q = mcδt Q=Thermal energy (measured in Joules) m=mass of the liquid being heated C=The specific heat, in o C ΔT=Change in temperature (T f -T i ) You do not have to know this formula-just understand that the amount of heat transferred is related to how large the object is, how much energy it requires to heat, and the temperature!!

25 Bellringer Day 04 Label the phase change diagram below to the best of your ability, showing how heat is transferred. You can use your notes to help.

26 Kinetic vs. Potential Energy KINETIC AND POTENTIAL ENERGY, MECHANICAL ENERGY, AND SYSTEMS

27 Types of Energy We ve discussed energy in the form of heat (thermal energy), but energy comes in many forms. The seven forms of energy are: thermal, chemical, electrical, nuclear, sound, radiant, and mechanical-we will be focusing for the remainder of the unit on mechanical! Energy can change between these forms. Remember the Law of Conservation of Energy: Energy cannot be created or destroyed. It can only be transformed from one type to another or passed from one object to another.

28 Kinetic Energy Kinetic energy is energy of motion The kinetic energy of an object is dependent on its mass and velocity KE = ½ mv 2 KE=Kinetic Energy m=mass v=velocicy Energy is measured in a unit called Joules (J)

29 Solving for Kinetic Energy Find the kinetic energy of a 10 kg bowling ball that is rolling at 3 m/s GIVEN KE = ½ mv 2 KE=? m=10kg v=3m/s SOLVE KE = ½ mv 2 KE = ½ (10) (3) 2 KE = ½ (10) (9) KE = ½ (90) KE = 45 J

30 Potential Energy Potential Energy is energy stored in an object It is related to the object s position

31 Gravitational Potential Energy Gravitational Potential Energy (PE g ) is energy stored in objects that can fall PE g = mgh PE g =Potential Energy m=mass g=gravity h=height Remember, on Earth g=9.8 m/s 2

32 Solving for Potential Energy Tanner s Coke can sits on his desk, 1 m above the floor. The mass of the can is 0.5 kg. Find its PE g GIVEN PE g = mgh PE g =? m=0.5kg SOLVE PE g = mgh PE g = (.5)(9.8)(1) PE g = 4.9 J g=9.8m/s 2 h=1m

33 Comparing Potential and Kinetic Energy Remember, energy is converted from one form to another For a falling object, the potential energy will decrease as the height decreases For that same falling object, the kinetic energy will increase because gravity increases The energy changes from potential to kinetic!

34 Mechanical Energy Mechanical energy is the total amount of kinetic and potential energy in a system A system is a group of objects that work together

35 Conserving Energy The law of the conservation of energy essentially means that the amount of energy in the universe does not change It describes what happens to energy as it is transformed from one type to another-even in situations where energy seems like it is not being conserved, it is! It is always transformed. The total amount of energy always stays the same.

36 Friction So what is causing us to lose mechanical energy? Friction! Friction changes kinetic energy to heat energy, which is lost to the surroundings Example: A swing set-if the energy of the swing decreases, the energy lost must be gained in another object. In this case, friction with the chains and hooks of the swing and air resistance cause mechanical energy to change to thermal energy So, while it may appear that the swing is losing energy, it s really just transferring it to a different form!

37 Conserving Energy Some systems are designed to reduce friction and conserve energy Pendulums and rollercoasters are systems that generally conserve mechanical energy Energy is transformed between gravitational potential and kinetic

38 Unit Project: Mouse Trap Racecars!

39 Bellringer Day 05 What is the kinetic energy of a 150kg object that is moving with a speed of 15m/s? Formula: KE = ½ mv 2

40 Work and Power COMPARING WORK AND POWER

Work In physics, work is the transfer of energy that occurs when a force makes an object move In order for work to be done, an applied force must make an object move, and the force must be in the

41 Work In physics, work is the transfer of energy that occurs when a force makes an object move In order for work to be done, an applied force must make an object move, and the force must be in the same direction as the object Example: You pick up a stack of books of the floor. You are applying force in the direction the books are moving. Work is being done. If you are holding the books in your arms, force is being applied but the books are not moving. No work is being done.

42 Work and Energy When work is done on an object, the result is an increase in its energy and is accompanied by a decrease in energy somewhere else. If something has energy, it can transfer energy to another object by doing work on that object Example: You carry a box. Chemical energy from your muscles is transferred to the box. Energy is always transferred from the object doing the work to the object on which work is done.

43 Calculating Work The amount of work done depends on the amount of force exerted and the distance over which the force is applied. W=Fd W=Work (in Joules) F=Force (in Newtons) d=distance (in meters) Work is measured in Joules-it is a measure of energy!

44 Solving for Work Brett s backpack weighs 30 N. How much work is done on the backpack when he lifts it 1.5 m from the floor to his back? GIVEN W=Fd SOLVE W=Fd W=? F=30N W=(30)(1.5) W=45J D=1.5m

45 Bellringer Day 06 A dancer lifts a 40 kg ballerina 1.4 m in the air and walks forward 2.2 m. How much work is done on the ballerina during and after the lift? Formulas: W=Fd; F=ma

46 Case Study: Power Imagine you and a friend are both pushing boxes up a ramp. The boxes weigh the same. Your friend is able to push the box faster than you, taking 30 seconds to push compared to your 45 seconds. What is happening here? You and your friend both moved the equal weight boxes the same distance-you both performed the same amount of work on the box The difference here is the time-your friend has more power than you do!

47 Power Power is the amount of work done in one second. It is a rate-the rate at which work is done!

48 Calculating Power Power is the relationship between the work done and the time it takes to do the work. P=W/t P=Power (in Watts) W=Work (in Joules); W=Fd t=time (in seconds) The unit for Power is Watts!

49 Solving for Power You do 900 J of work in pushing a sofa. If it took 5s to move the sofa, what was your power? GIVEN P=W/t W=900 J t=5s SOLVE P=W/t P= (900)/(5) P= 180 W

50 Bellringer Day 07 The power produced by an electric motor is 500 W. How long will it take the motor to do 10,000 J of work? Formula: P=W/t

51 Simple Machines INCLINED PLANES, LEVERS, AND MECHANICAL ADVANTAGE

52 Machines A machine is a device that makes doing work easier Changes the size and/or direction of the exerted force They do not make less work; they make it easier to work All simple machines can be categorized as an inclined plane or a lever

53 Inclined Plane An inclined plane is a sloping surface used to raise objects

54 Variations of the Inclined Plane WEDGE A wedge is a moving inclined plane with 1 or 2 sloping sides SCREW A screw is an inclined plane wrapped in a spiral around a cylinder

55 Lever A lever is a bar that is free to pivot around a fixed point (fulcrum)

56 Variations of the Lever PULLEY A grooved wheel with a rope or chain running along the groove WHEEL AND AXEL Two wheels of different sizes that rotate together; a pair of rotating levers

57 Work Input vs. Work Output The force applied to the machine is called the input force What you do The input force is represented by the abbreviation F in The force applied by the machine is called the output force What the machine does The output force is represented by the abbreviation F out The work the machine applies to the object cannot be more than the work you apply to the machine-remember, energy cannot be created or destroyed! However, work input is always more than work output, because some of that energy transfers to heat energy due to friction

58 Mechanical Advantage The ratio of the output force to the input force is the mechanical advantage of the machine There are two types of mechanical advantage: Ideal Mechanical Advantage (IMA): the mechanical advantage of a machine without friction Actual Mechanical Advantage (AMA): number of times a machine increases the effort force IMA=d E /d R Effort/Resistance AMA=F R /F E Resistance Force/Effort Force

59 Solving for Mechanical Advantage You use a 160 cm plank to lift a large rock. If the rock is 20 cm from the fulcrum, what is the plank s IMA? GIVEN IMA=d E /d R L E /L R L E (effort) = 160 L R (resistance) =20 SOLVE IMA= L E /L R IMA = 160/20 IMA = 8 IMA =?

60 Solving for Mechanical Advantage A worker applies an effort force of 20 N to open a window with a resistance force of 500 N. What is the crowbar s AMA? GIVEN SOLVE AMA= F R /F E F R = 500 N F E = 20 N AMA =? AMA= F R /F E AMA = 500/20 IMA = 25

61 Bellringer Day 08 Find the effort force needed to lift a 2000 N rock using a jack with a mechanical advantage of 10. Formula: AMA= FR/FE

62 Efficiency EFFICIENCY OF MACHINES

63 Efficiency of Machines Efficiency is a measure of how much work put into a machine is changed into useful output work by the machine High efficiency machines produce less heat and friction In an ideal machine, the input work equals the output work and there is no friction. An ideal machine has an efficiency of 100% In a real machine, friction always causes the output work to be less than the input work. The efficiency of a real machine is always less than 100%

64 Calculating Efficiency Efficiency is a relationship between the output work and input work. E=W out /W in x 100 E=Efficiency W out =output work (in J) W in =input work (in J) Remember, no machine is 100% efficient!

65 Solving for Efficiency Find the efficiency of a machine that does 800J of work if the input work is 2,400 J. GIVEN E = W out /W in x 100 E =? W out = 800 J SOLVE E = W out /W in x 100 E = (800)/(2400) x 100 E = 33.3% W in = 2,400 J

66 Bellringer Day Explain why no machine can be 100% efficient. 2. Find the mechanical advantage of a hammer if the input force is 125 N and the output force is 2,000 N. Formula: AMA= F R /F E

67 Bellringer Day Explain the Law of the Conservation of Energy. 2. A person places a metal spoon that is at room temperature into a bowl of hot soup. How will the thermal energies of the spoon and the soup be affected? a) The spoon will increase in thermal energy, and the soup will decrease in thermal energy. b) Both the spoon and the soup will increase in thermal energy. c) The spoon will decrease in thermal energy, and the soup will increase in thermal energy. d) Both the spoon and the soup will decrease in thermal energy

68 Mouse Trap Racecars!

69 Bellringer Day How much potential energy does a 55-kg person gain when she walks to the top of a hill 20 m tall? Formula: PE g = mgh 2. An object has a mass of 12.8 kg and a velocity of 8.4 m/s. What is the kinetic energy of the object? Formula: KE = ½ mv 2

70 Day 12: Test Day Thermal Energy Energy Transfer Kinetic vs. Potential Energy Mechanical Energy Simple Machines Efficiency

Physical Science midterm study guide. Chapter 1 and 2

Physical Science midterm study guide Chapter 1 and 2 1. Explain the difference between a scientific law and a scientific theory a. Laws generalize observations b. Theories explain observations 2. Select