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ENERGY AND WORK SPH4C/SPH3U Findlay. Energy  Energy can be defined as the capacity to work or to accomplish a task.  Example: burning fuel allows an.

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Presentation on theme: "ENERGY AND WORK SPH4C/SPH3U Findlay. Energy  Energy can be defined as the capacity to work or to accomplish a task.  Example: burning fuel allows an."— Presentation transcript:

1 ENERGY AND WORK SPH4C/SPH3U Findlay

2 Energy  Energy can be defined as the capacity to work or to accomplish a task.  Example: burning fuel allows an engine to do the work of moving a car.

3 Forms of Energy  Radiant Energy  Components of the electromagnetic spectrum have characteristics of waves, such as wavelengths, frequencies, and energies; they travel in a vacuum at the speed of light (3.0 x 10 8 m/s).

4 Forms of Energy  Kinetic Energy  Energy of motion, every moving object has this energy

5 Forms of Energy  Gravitational Potential Energy  A raised object has stored energy due to its position above some reference level

6 Forms of Energy  Elastic Potential Energy  Is stored in objects that are stretched or compressed.

7 Forms of Energy  Chemical Potential Energy  In chemical reactions, new molecules are formed and chemical potential energy is released or absorbed.

8 Forms of Energy  Nuclear Potential Energy  The nucleus of every atom contains energy. Nuclear fission – The breaking down of atoms Nuclear fusion – the joining of atoms

9 Forms of Energy  Electrical Potential Energy  Electrons in a electric circuit can transfer energy to the components of the circuit.

10 Forms of Energy  Thermal Energy  The more rapidly atoms and molecules move, the greater their total thermal energy.

11 Forms of Energy  Sound Energy  Produced by vibrations; the energy travels by waves through a material to the receiver.

12 Energy Transformations  The 9 forms of energy listed above are able to change from one to another; this change is called energy transformation. A energy transformation equation can be used to summarize the changes in a transformation. Example: a microwave  Electrical energy  Radiant Energy  Thermal Energy

13 Energy Transformation Technology  A device used to transform energy for a specific purpose.

14 Mechanical Work  Mechanical work is done on an object when a force displaces the object in the direction of the force or a component of the force.  Work is not energy itself, but rather it is a transfer of mechanical energy.

15 Mechanical Work

16 Is this an example of work?  A teacher applies a force to a wall and becomes exhausted.  A book falls of a table and free falls to the ground.  A waiter carries a tray full of meals above his head by one arm straight across the room at constant speed.

17 Example: Pushing a cart How much mechanical work does a store manager do on a grocery cart if she applies a force with magnitude 25 N in the forward direction and displaces the cart 3.5 m in the same direction?

18 Example: Work done to change the speed A curler applies a force of 15 N on a curling stone and accelerates the stone from rest to a speed of 8.00 m/s in 3.5 s. Assuming that the ice surface is level and frictionless, how much mechanical work does the curler do on the stone?

19 Negative Work

20 Work Done by Friction

21 Example A toboggan carrying two children (total mass 85kg) reaches its maximum speed at the bottom of a hill. It then glides to a stop 21 m along a horizontal surface. The coefficient of friction between the toboggan and the snowy surface is 0.11. A. Calculate the magnitude of the force of kinetic friction acting on the toboggan B. Calculate the work done by the force of kinetic friction on the toboggan

22 Example

23 Friction  The work done by friction has been transformed into thermal energy. This is observed as a increase in temperature.

24 Zero Work  Sometimes an object can experience a force, a displacement, or both, yet no work is done on the object.  Example: Holding a box in your hands. The box is not moving so no work is done so the displacement is zero.  A puck on an air hockey table is moving but it does not have force acting parallel to the movement as friction is negligible.

25 Positive, Negative, or Zero?

26 Force and Displacement in Different Directions  An object may experience a force in one direction while it moves in a different direction. This occurs when a person pulls on a suitcase with wheels and a handle.

27 Horizontal Component causes Horizontal Displacement

28 Example  Calculate the mechanical work done by a custodian on a vacuum cleaner if the custodian exerts an applied force of 50.0 N on the vacuum hose and the hose makes a 30.0 o with the floor. The vacuum cleaner moves 3.00 m to the right on a level, flat surface.

29 Total Work Done by Many Forces

30 Example A shopper pushes a shopping cart on a horizontal surface with horizontal applied force of 41.0 N for 11.0 m. The cart experiences a force of friction of 35.0 N. Calculate the total mechanical work done on the shopping cart.

31 MECHANICAL ENERGY SPH4C/SPH3U Findlay

32 Work  Energy is the capacity to do work and provides objects with the ability to do work.  Work is not energy itself, but rather a transfer of energy.  A force does work on an object if it causes the object to move.  Work is always done on an object and results in a change in the object.  The work done is equal to the change in energy.

33 Mechanical Energy

34 Kinetic and Potential Energy  Kinetic energy is the energy of motion and potential energy is the energy to, potentially, do something else.

35 Kinetic Energy  Energy due to the motion of an object.

36 Kinetic Energy

37 Change in Energy

38

39 Kinetic Energy

40 Example A car of mass 1500 kg is travelling at a speed of 24 m/s. Calculate the kinetic energy of the car.

41 Example An object of mass 5.0 kg is travelling at a speed of 4.0 m/s. 27 J of work is done to increase the speed of the object. Calculate its final kinetic energy and final speed.

42 Gravitational Potential Energy  The type of energy that an object possess because of its position above some level.  The energy is called potential because it can be stored and used at a lower level for work.  When an object falls, its potential energy is transformed into kinetic energy as its speed increases.

43 Gravitational Potential Energy

44  The potential energy in a system must be based against a Reference Level – The level to which the object may fall.  It is important to note that when answering questions about relative potential energy, it is important to state the reference level.

45 Example In the sport of pole vaulting, the jumper’s point of mass centralization, called the centre of mass, must clear the pole. Assume that a 59 kg jumper must raise the centre of mass 1.1 m off the ground to 4.6 m off the ground. What is the jumper’s gravitational potential energy at the top of the bar relative to the point at which the jumper started the jump?

46 Example

47 Mechanical Energy


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