1. Science Essay December 14th
You will have time to work on the science research paper this Friday

2. Due Friday Class –> resources
On separate sheet, include a work cited of your source material
Utilize primary (recommended) and secondary documents that provide factual information : 5 sources or more
All scholarly, scientific sources
Attribute quotes and any ideas that are not your own within the body of the essay (in text citations)

3. Good places to find scholarly science articles:
Use the search filters:
Search for articles that can be read online or have the pdf (full version available)
Search in science journals
Search for resent articles (past 10 years)

4. Resources for Finding and Accessing Scientific Papers
projects/top_science- fair_finding_scientific_papers.shtml

5. Physics Final It will Includes Chapter 5 Similar Format as other Tests
Period 1 & 2 Monday December 19th
Period 3 & 4 Tuesday December 20th
Period 5 & 6 Wednesday December 21st
Winter Break starts Thursday December 22 until January 9th

7. Work and Energy audiokinetic sculpture

8. Chapter 5: Work, Energy, Power8

9. Objectives .
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. 9

10. Todays objective
Recognize the difference between the scientific and ordinary definitions of work.
Define work by relating it to force and displacement.
Identify where work is being performed in a variety of situations.
Calculate the net work done when many forces are applied to an object.

11. Work In physics, work has a very specific meaning.
In physics, work represents a measurable change in a system, caused by a force.

12. WORK Physical Quantities Symbols Units Brief Definition Work W
Joule: J
A form of mechanical energy transfer.

13. In order to accomplish work on an object there must be a force exerted on the object and it must move in the direction of the force.

14. 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.

15. Work (force is parallel to distance)
Force (N)
Work (joules)
W = F x d
Distance (m)

16. Work (force at angle to distance)
Force (N)
Work (joules)
W = Fd cos (q)
Angle
Distance (m)

18. When a force does no work

22. Work done against gravity
Mass (g)
Height object raised (m)
Work (joules)
W = mgh
Gravity (m/sec2)

24. A tugboat pulls a ship with a constant net horizontal force of 5
A tugboat pulls a ship with a constant net horizontal force of 5.00 × 103 N and causes the ship to move through a harbor. How much work is done on the ship if it moves a distance of 3.00 km?
A weight lifter lifts a set of weights a vertical distance of 2.00 m. If a constant net force of 350 N is exerted on the weights, what is the net work done on the weights?
A shopper in a supermarket pushes a cart with a force of 35 N directed at an angle of 25° downward from the horizontal. Find the work done by the shopper on the cart as the shopper moves along a 50.0 m length of aisle.
If 2.0 J of work is done in raising a 180 g apple, how far is it lifted?

26. 1) For each of the following cases, indicate whether the work done on the second object in each example will have a positive or a negative value.
a. The road exerts a friction force on a speeding car skidding to a stop.
b. A rope exerts a force on a bucket as the bucket is raised up a well.
c. Air exerts a force on a parachute as the parachutist falls to Earth.

27. 2) If a neighbor pushes a lawnmower four times as far as you do but exerts only half the force, which one of you does more work and by how much?

28. A worker pushes a 1.50 × 103 N crate with a horizontal force of 345 N a distance of 24.0 m. Assume the coefficient of kinetic friction between the crate and the floor is
How much work is done by the worker on the crate?
b. How much work is done by the floor on the crate?
c. What is the net work done on the crate?

30. A kg ball in a kinetic sculpture moves at a constant speed along a motorized vertical conveyor belt. The ball rises 1.32 m above the ground. A constant frictional force of N acts in the direction opposite the conveyor belt’s motion.
What is the net work done on the ball?

32. https://archive.org/details/The_Mechanical_Unive rse_and_Beyond_13_Conservation_of_Energy

33. Conceptual
1)Give an example of something we think of as work in everyday circumstances that is not work in the scientific sense. Is energy transferred or changed in form in your example? If so, explain how this is accomplished without doing work.
2)Give an example of a situation in which there is a force and a displacement, but the force does no work. Explain why it does no work.
3) Describe a situation in which a force is exerted for a long time but does no work. Explain.

34. Energy and Conservation of Energy
Investigation Key Question:
How is motion on a track related to energy? 34

35. Energy and Conservation of Energy
Energy describes a system’s ability to cause 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.

36. Different 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.

37. The workings of the universe can be viewed as energy flowing from one place to another and changing back and forth from one form to another.

38. Potential Energy
Objects that have potential energy do not use the energy until they move.
An object’s potential energy comes from the gravity of Earth.
Technically, energy from height is called gravitational potential energy.
Other forms of potential energy also exist, such as potential energy stored in springs.

39. Potential Energy Ep = mgh Mass (kg) Potential Energy (joules)
Height (m)
Acceleration
of gravity (m/sec2)

40. Calculating 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?
You are asked for potential energy and time.
You are given mass, height and work done per second.
Use: Ep = mgh.
Solve for Ep = (102 kg) (9.8 N/kg) (4 m) = 3,998 J.
At a rate fof 50 J/s, it takes 80 s to push the cart up the ramp.

41. 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.

42. 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).

43. Kinetic Energy Ek = 1 mv2 2 Mass (kg) Kinetic Energy Speed (m/sec)
(joules)
Ek = 1 mv2 2
Speed (m/sec)

44. Kinetic Energy
Kinetic energy becomes important in calculating braking distance.

45. The formula for kinetic energy
A force (F) is applied to mass (m) and
creates acceleration (a).
After a distance (d), the ball has reached speed (v), therefore the work done is its mass times acceleration time distance:
W= fd = (ma) x d = mad
Also: d = ½ at2
Replace d in the equation for work, combine similar terms:
W= ma (½ at2) = ½ ma2t2
Also: v = at, so v2 = a2t2
Replace a2t2 by v2 shows that the resulting work is the formula for kinetic energy:
W = ½ mv2

46. Calculating kinetic energy
A car with a mass of 1,300 kg is going straight ahead at a speed of 30 m/s (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.
You are asked for kinetic energy and stopping distance
You are given mass, speed and force of brakes.
Use Ek = 1/2mv2 and W= fd
Solve for Ek = ½ (1,300 kg) ( 30 m/s)2 = 585,000 J
To stop the car, work done by brakes = Ek of car, so W = Ek
Solve for distance = W ÷ f = 585,000J ÷ 9,500 N = 62 m

47. 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.

48. Energy in a closed system
The conservation of energy is most useful when it is applied to a closed system.
Because of the conservation of energy, the total amount of matter and energy in your system stays the same forever.

49. Energy in a closed system
The total energy in the system is the potential energy of the ball at the start.
Later, the ball is at a lower height (h) moving with speed (v) and has both potential and kinetic energy.

50. Hydroelectric Power
Every day in the United States the average person uses about 90 million joules of electrical energy.
This energy comes from many sources, including burning coal, gas and oil, nuclear power, and hydroelectric power.
In hydroelectric power, the potential energy of falling water is converted to electricity.
No air pollution is produced, nor hazardous wastes created.