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Unit 4, Chapter 10. CPO Science Foundations of Physics. Chapter 9. Unit 4: Energy and Momentum. Chapter 10 Work and Energy. 10.1 Machines and Mechanical Advantage 10.2 Work 10.3 Energy and Conservation of Energy. Chapter 10 Objectives.

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unit 4 chapter 10
Unit 4, Chapter 10

CPO Science

Foundations of Physics

Chapter 9

unit 4 energy and momentum
Unit 4: Energy and Momentum

Chapter 10 Work and Energy

  • 10.1 Machines and Mechanical Advantage
  • 10.2 Work
  • 10.3 Energy and Conservation of Energy
chapter 10 objectives
Chapter 10 Objectives
  • Calculate the mechanical advantage for a lever or rope and pulleys.
  • Calculate the work done in joules for situations involving force and distance.
  • Give examples of energy and transformation of energy from one form to another.
  • Calculate potential and kinetic energy.
  • Apply the law of energy conservation to systems involving potential and kinetic energy.
chapter 10 vocabulary terms
Chapter 10 Vocabulary Terms
  • machine
  • energy
  • input force
  • output force
  • thermal energy
  • ramp
  • gear
  • screw
  • rope and pulleys
  • closed system
  • work
  • lever
  • friction
  • mechanical system
  • simple machine
  • potential energy
  • kinetic energy
  • radiant energy
  • nuclear energy
  • chemical energy
  • mechanical energy
  • mechanical advantage
  • joule
  • pressure
  • energy
  • conservation of energy
  • electrical energy
  • input output
  • input arm output
  • arm
  • fulcrum
10 1 machines and mechanical advantage
Key Question:

How do simple machines work?

10.1 Machines and Mechanical Advantage

*Students read Section 10.1 AFTER Investigation 10.1

10 1 machines
10.1 Machines
  • The ability of humans to build buildings and move mountains began with our invention of machines.
  • In physics the term “simple machine” means a machine that uses only the forces directly applied and accomplishes its task with a single motion.
10 1 machines1
10.1 Machines
  • The best way to analyze what a machine does is to think about the machine in terms of input and output.
10 1 mechanical advantage
10.1 Mechanical Advantage
  • Mechanical advantage is the ratio of output force to input force.
  • For a typical automotive jack the mechanical advantage is 30 or more.
  • A force of 100 newtons (22.5 pounds) applied to the input arm of the jack produces an output force of 3,000 newtons (675 pounds)— enough to lift one corner of an automobile.
10 1 mechanical advantage1
10.1 Mechanical Advantage

Output force (N)

MA = Fo

Fi

Mechanical

advantage

Input force (N)

10 1 mechanical advantage of a lever
10.1 Mechanical Advantage of a Lever

Length of input arm

(m)

Mechanical

advantage

MAlever = Li

Lo

Length of output arm

(m)

10 1 calculate position
10.1 Calculate position
  • Where should the fulcrum of a lever be placed so one person weighing 700 N can lift the edge of a stone block with a mass of 500 kg?
  • The lever is a steel bar three meters long.
  • Assume a person can produce an input force equal to their own weight.
  • Assume that the output force of the lever must equal half the weight of the block to lift one edge.
10 1 wheels gears and rotating machines
10.1 Wheels, gears, and rotating machines
  • Axles and wheels provide advantages.
  • Friction occurs where the wheel and axle touch or where the wheel touches a surface.
  • Rolling motion creates less wearing away of material compared with two surfaces sliding over each other.
  • With gears the trade-off is made between torque and rotation speed.
  • An output gear will turn with more torque when it rotates slower than the input gear.
10 1 ramps and screws
10.1 Ramps and Screws
  • Ramps reduce input force by increasing the distance over which the input force needs to act.
  • A screw is a simple machine that turns rotating motion into linear motion.
  • A thread wraps around a screw at an angle, like the angle of a ramp.
10 2 work
Key Question:

What are the consequences of multiplying forces in machines?

10.2 Work

*Students read Section 10.2 AFTER Investigation 10.2

10 2 work1
10.2 Work
  • In physics, work has a very specific meaning.
  • In physics, work represents a measurable change in a system, caused by a force.
10 2 work2
10.2 Work
  • If you push a box with a force of one newton for a distance of one meter, you have done exactly one joule of work.
10 2 work force is parallel to distance
10.2 Work (force is parallel to distance)

Force (N)

W = F x d

Work (joules)

Distance (m)

10 2 work force at angle to distance
10.2 Work (force at angle to distance)

Force (N)

Work (joules)

W = Fd cos (q)

Angle

Distance (m)

10 2 work done against gravity
10.2 Work done against gravity

Mass (g)

Height object raised (m)

W = mgh

Work (joules)

Gravity (m/sec2)

10 3 calculate work
A crane lifts a steel beam with a mass of 1,500 kg.

Calculate how much work is done against gravity if the beam is lifted 50 meters in the air.

How much time does it take to lift the beam if the motor of the crane can do 10,000 joules of work per second?

10.3 Calculate work
10 3 energy and conservation of energy
10.3 Energy and Conservation of Energy
  • Energy is the ability to make things change.
  • A system that has energy has the ability to do work.
  • Energy is measured in the same units as work because energy is transferred during the action of work.
10 3 forms of energy
10.3 Forms of Energy
  • Mechanical energy is the energy possessed by an object due to its motion or its position.
  • Radiant energy includes light, microwaves, radio waves, x-rays, and other forms of electromagnetic waves.
  • Nuclear energy is released when heavy atoms in matter are split up or light atoms are put together.
  • The electrical energy we use is derived from other sources of energy.
10 3 potential energy
10.3 Potential Energy

Mass (kg)

Ep = mgh

Potential Energy

(joules)

Height (m)

Acceleration

of gravity (m/sec2)

10 3 potential energy1
10.3 Potential Energy
  • A cart with a mass of 102 kg is pushed up a ramp.
  • The top of the ramp is 4 meters higher than the bottom.
  • How much potential energy is gained by the cart?
  • If an average student can do 50 joules of work each second, how much time does it take to get up the ramp?
10 3 kinetic energy
10.3 Kinetic Energy
  • Energy of motion is called kinetic energy.
  • The kinetic energy of a moving object depends on two things: mass and speed.
  • Kinetic energy is proportional to mass.
10 3 kinetic energy1
10.3 Kinetic Energy
  • Mathematically, kinetic energy increases as the square of speed.
  • If the speed of an object doubles, its kinetic energy increases four times. (mass is constant)
10 3 kinetic energy2
10.3 Kinetic Energy

Mass (kg)

Speed (m/sec)

Ek = 1 mv2

2

Kinetic Energy

(joules)

10 3 kinetic energy3
10.3 Kinetic Energy
  • Kinetic energy becomes important in calculating braking distance.
10 3 calculate kinetic energy
10.3 Calculate Kinetic Energy
  • A car with a mass of 1,300 kg is going straight ahead at a speed of 30 m/sec (67 mph).
  • The brakes can supply a force of 9,500 N.
  • Calculate:

a) The kinetic energy of the car.

b) The distance it takes to stop.

10 3 law of conservation of energy
10.3 Law of Conservation of Energy
  • As energy takes different forms and changes things by doing work, nature keeps perfect track of the total.
  • No new energy is created and no existing energy is destroyed.
10 3 energy and conservation of energy1
Key Question:

How is motion on a track related to energy?

10.3 Energy and Conservation of Energy

*Students read Section 10.3 BEFORE Investigation 10.3