Bellringer #51 Read “Careers Using Physics” on page 427 Read “Careers Using Physics” on page 427 Answer both questions in your journal Answer both questions in your journal Leave your books out and open Leave your books out and open

Bellringer #45 Read “What Machines are used on Bicycles” on page 435 Read “What Machines are used on Bicycles” on page 435 Answer both questions in your journal Answer both questions in your journal

What is work? Which picture shows someone who is working? Which picture shows someone who is working?

What is work? Work is being done when you Work is being done when you Push Push Lift Lift Throw Throw You do work when you move something from one place to another. You do work when you move something from one place to another. Your force makes the object move Your force makes the object move

What is work?

Work If you push on the wall is it work? If you push on the wall is it work?

Work is not done every time a force is applied. Work is not done every time a force is applied. A force must be exerted over a distance for it to be work. A force must be exerted over a distance for it to be work. The force must be applied in the direction of the object’s motion. The force must be applied in the direction of the object’s motion.

You pick up a bag of groceries. You pick up a bag of groceries. Your arms are applying a force on the bag to hold it up. Your arms are applying a force on the bag to hold it up. You carry the bag of groceries to the car. You carry the bag of groceries to the car. Have your arms done any work on the bag? Have your arms done any work on the bag?

What Is Work? Work is calculated by multiplying the force by the distance over which the force is applied. work = force x distance, or W = Fd Work is zero when an object is not moving. Work is measured in joules (J): 1 N m = 1 J = 1 kg m2/s2

Math Skills Imagine a father playing with his daughter by lifting her repeatedly in the air. How much work does he do with each lift if he lifts her 2.0 m and exerts an average force of 190 N? 1. Underline and label knowns and circle unknowns. 2. Write the equation for work. 1)W = f x d 2)W = 190 N x 2.0 m 3) W = 380 J 3. Insert the known values into the equation. the equation. 4. Solve.

Power Does running up the stairs require more power than walking up the stairs? Does running up the stairs require more power than walking up the stairs?

Power -a quantity that measures the rate at which work is done or energy is transformed or energy is transformed 〉 What is the relationship between work and power? 〉 Power is the rate at which work is done, or how much work is done in a given amount of time. Power is measured in watts (W): 1 W = 1 J/s

Watts the matter with you ? Watt expresses electric power. Watt expresses electric power. A 50-watt light bulb does the work at a rate of 50 joules per second. A 50-watt light bulb does the work at a rate of 50 joules per second. Large quantities of power are measured in kilowatts (kW) Large quantities of power are measured in kilowatts (kW) 1 kilowatt = 1000 watts 1 kilowatt = 1000 watts

A bulldozer has more power than a person with a shovel. A bulldozer has more power than a person with a shovel. If a bulldozer and a person were working for 1 hour. Which would do more work? If a bulldozer and a person were working for 1 hour. Which would do more work?

Math Skills Lifting an elevator 18 m takes 100 kJ. If doing so takes 20 s, what is the average power of the elevator during the process? 1. Underline and label knowns and circle unknowns. 2. Write the equation for power. 3. Insert the known values into the equation. the equation. 4. Solve. P = work time time P = 1 x 10 5 J 20 s 20 s

Machines and Mechanical Advantage 〉 How do machines make work easier? 〉 Machines help do work by changing the size of an input force, the direction of the force, or both. mechanical advantage: a quantity that expresses how much a machine multiplies force or distance

Math Skills Mechanical Advantage Calculate the mechanical advantage of a ramp that is 5.0 m long and 1.5 m high. mechanical advantage = 5.0 m 1.5 m Mechanical advantage = 3.3

Efficiency of Machines Not all of the work done by a machine is useful work. because of friction, work output < work input Efficiency is the ratio of useful work out to work in. Efficiency - a quantity, usually expressed as a percentage, that measures the ratio of useful work output to work input

Math Skills A sailor uses a rope and an old, squeaky pulley to raise a sail that weighs 140 N. He finds that he must do 180 J of work on the rope to raise the sail by 1 m. (He does 140 J of work on the sail.) What is the efficiency of the pulley? Express your answer as a percentage. Efficiency

Bellringer #46 Make a table in your journal that looks like this Make a table in your journal that looks like this You will be watching a clip and writing down all of the examples of the following simple machines that are discussed in the clip. You will be watching a clip and writing down all of the examples of the following simple machines that are discussed in the clip. Incline PlaneWedgeScrew

What Are Simple Machines? Simple machines are divided into two families: the lever family and the inclined plane family. Simple machines are divided into two families: the lever family and the inclined plane family. Lever family: simple lever simple lever pulley pulley wheel and axle wheel and axle Inclined plane family: simple inclined plane simple inclined plane wedge wedge screw screw

C:\Physical Science \Physical Science 2\Phys. Sci. Movies\ch. 13 (best)Work__Energy__and_the_Simple_M achine__Lever__Wheel_and_Axle__Pulle y_.asf C:\Physical Science \Physical Science 2\Phys. Sci. Movies\ch. 13 (best)Work__Energy__and_the_Simple_M achine__Lever__Wheel_and_Axle__Pulle y_.asf C:\Physical Science \Physical Science 2\Phys. Sci. Movies\ch. 13 (best)Work__Energy__and_the_Simple_M achine__Lever__Wheel_and_Axle__Pulle y_.asf C:\Physical Science \Physical Science 2\Phys. Sci. Movies\ch. 13 (best)Work__Energy__and_the_Simple_M achine__Lever__Wheel_and_Axle__Pulle y_.asf

The Lever Family 〉 Two principal parts of all levers? 〉 All levers have a rigid arm that turns around a point called the fulcrum. Levers are divided into three classes. Levers are divided into three classes.

Pulleys are modified levers. Pulleys are modified levers. The point in the middle of a pulley is like the fulcrum of a lever. The point in the middle of a pulley is like the fulcrum of a lever. The rest of the pulley behaves like the rigid arm of a first-class lever. The rest of the pulley behaves like the rigid arm of a first-class lever. A wheel and axle is a lever or pulley connected to a shaft. A wheel and axle is a lever or pulley connected to a shaft. Screwdrivers and cranks are common wheel-and-axel machines. Screwdrivers and cranks are common wheel-and-axel machines. The Lever Family, continued

C:\Physical Science \Physical Science 2\Phys. Sci. Movies\ch. 13 (best) Work__Energy__and_the_Simple_Machin e__Inclined_Plane__Wedge__Screw_.asf C:\Physical Science \Physical Science 2\Phys. Sci. Movies\ch. 13 (best) Work__Energy__and_the_Simple_Machin e__Inclined_Plane__Wedge__Screw_.asf C:\Physical Science \Physical Science 2\Phys. Sci. Movies\ch. 13 (best) Work__Energy__and_the_Simple_Machin e__Inclined_Plane__Wedge__Screw_.asf C:\Physical Science \Physical Science 2\Phys. Sci. Movies\ch. 13 (best) Work__Energy__and_the_Simple_Machin e__Inclined_Plane__Wedge__Screw_.asf

The Inclined Plane Family 〉 How does using an inclined plane change the force required to do work? 〉 Pushing an object up an inclined plane requires less input force than lifting the same object does.

Wedge - is a modified inclined plane. Screw - is an inclined plane wrapped around a cylinder. Pitch M.A. = Pitch / Distance

Compound Machines compound machine: a machine made of more than one simple machine

Homework Chapter 13 S.2 Concept Review and Quiz Chapter 13 S.2 Concept Review and Quiz

Bellringer # 44 How do you think the Egyptians built the pyramids? (hint: think about simple machines) How do you think the Egyptians built the pyramids? (hint: think about simple machines)

Ideal MA = input distance/ output distance Ideal MA = input distance/ output distance Actual MA= output force/ input force Actual MA= output force/ input force % Efficiency= actual MA/ ideal MA x 100 % Efficiency= actual MA/ ideal MA x 100 Output force And Distance Input force and distance

Homework Section 2 Review Questions page 443 Section 2 Review Questions page 443 #1-8 #1-8

Bellringer #48 Read “Energy Stored in Plants” on page 451 Read “Energy Stored in Plants” on page 451 Answer both questions in your journal. Answer both questions in your journal.

Bellringer #48 Make a table in your journal that looks like this Make a table in your journal that looks like this You will be watching a clip and writing down all of the examples of the following simple machines that are discussed in the clip. You will be watching a clip and writing down all of the examples of the following simple machines that are discussed in the clip. Wheel and AxlePulleyLever

Is work being done?

Energy and Work What is the relationship between energy and work? Whenever work is done, energy is transformed or is transferred from one system to another system. energy: the capacity to do work Energy is measured in joules (J).

If something does not move, has work happened? If something does not move, has work happened? If something does not move, is energy present? If something does not move, is energy present?

Why Joules? Energy can be calculated by how much work is done on the object that energy is transferred to. Energy can be calculated by how much work is done on the object that energy is transferred to. Work and Energy are expressed as Joules Work and Energy are expressed as Joules

Potential Energy - the energy that an object has because of the position, shape, or condition of the object Any object that is stretched or compressed to increase or decrease the distance between its parts has elastic potential energy. Examples: stretched bungee cords, compressed springs

Any system of two or more objects separated by a vertical distance has gravitational potential energy. Any system of two or more objects separated by a vertical distance has gravitational potential energy. Example: a roller coaster at the top of a hill Example: a roller coaster at the top of a hill

Gravitational potential energy depends on both mass and height. grav. PE = mass  free-fall acceleration  height, or PE = mgh PE = mgh The height can be relative. Math Skills A 65 kg rock climber ascends a cliff. What is the climber’s gravitational potential energy at a point 35 m above the base of the cliff?

1) PE = mgh 2) PE = (65 kg)(9.8 m/s 2 )(35 m) 3) PE = 2.2  10 4 kgm 2 /s 2 4) PE = 2.2  10 4 J Math Skills

Kinetic Energy - the energy of an object due to the object’s motion Kinetic energy depends on both the mass and the speed of an object. Equation: KE = ½  mass  speed squared, or KE= ½mv 2

Math Skills Kinetic Energy What is the kinetic energy of a 44 kg cheetah running at 31 m/s? 1. Underline and label the given values and circle the unknown values. 2. Write the Equation 3. Insert the known values into the equation 4. Solve KE = ½ (44 kg)(31 m/s)2 = 2.1 × 10 4 kgm2/s2 KE = 2.1 × 10 4 J

Other Forms of Energy 1.mechanical energy - the amount of work an object can do because of the object’s kinetic and potential energies. 2. nonmechanical energy - Energy that lies at the level of the atom. 3. chemical energy - Chemical reactions involve potential energy.

Other Forms of Energy 4. nuclear fusion - nuclear reactions within the sun 5. electric energy (energy stored a field) -Electrical energy results from the location of charged particles in an electric field. -When electrons move from an area of higher electric potential to an area of lower electric potential, they gain energy. 6. electromagnetic waves - Light energy traveling from the sun to Earth across empty space. - Electromagnetic waves are made electric and magnetic fields, so light energy is another example of energy stored in a field.

Homework S.3 Concept Review and Quiz S.3 Concept Review and Quiz

Study your vocab for 6 minutes Study your vocab for 6 minutes

Section 4: Conservation of Energy Energy Transformations Energy readily changes from one form to another. Potential energy can become kinetic energy. Potential energy can become kinetic energy. Example: As a roller coaster car goes down a hill, PE changes to KE. Example: As a roller coaster car goes down a hill, PE changes to KE. Kinetic energy can become potential energy. Kinetic energy can become potential energy. Example: The KE of a roller coaster car at the bottom of a hill can do work to carry it up another hill. Example: The KE of a roller coaster car at the bottom of a hill can do work to carry it up another hill. Mechanical energy can change to other forms of energy. Mechanical energy can change to other forms of energy.

Graphing Skills Graphing Mechanical Energy The bar graph shown here presents data about a roller coaster car. What variables are plotted? What variables are plotted? What does the legend tell you about this graph? What does the legend tell you about this graph?

1. Study the axes and legend to determine the variables. Location is the variable on the x-axis. Two variables are plotted on the y-axis: kinetic and potential energy.

2. Consider the relationship between the variables. The independent variable is location, because the car’s kinetic energy and potential energy change with location.

3. Examine the legend and how it relates to the graph. The legend indicates that the car’s mechanical energy consists of both kinetic energy and potential energy.

The Law of Conservation of Energy Energy cannot be created or destroyed. -In other words, the total amount of energy in the universe never changes, although energy may change from one form to another. 1.Energy does not appear or disappear. 2. Whenever the total energy in a system increases, it must be due to energy that enters the system from an external source. 3. Thermodynamics describes energy conservation. 4. For any system, the net change in energy equals the energy transferred as work and as heat. This form of the law of energy conservation is called the first law of thermodynamics.

The Law of Conservation of Energy, continued Systems may be open, closed, or isolated. Systems may be open, closed, or isolated. open system: energy and matter are exchanged with the open system: energy and matter are exchanged with the surroundings surroundings closed system: energy but not matter is exchanged closed system: energy but not matter is exchanged isolated system: neither energy nor matter is exchanged isolated system: neither energy nor matter is exchanged Most real-world systems are open. Most real-world systems are open.

Homework S.4 Review Questions S.4 Review Questions Pg.461 Pg.461 #1-9 #1-9

Bellringer #49 List the units (or a unit) for the following: List the units (or a unit) for the following: Speed = Speed = Distance = Distance = Time = Time = Acceleration = Acceleration = Force = Force = Mass = Mass = Momentum= Momentum= Weight = Weight = Work = Work = Power = Power = Mechanical Advantage = Mechanical Advantage = Energy = Energy = Efficiency = Efficiency =