Understanding+Concepts

Friday, November 13 Homework //Chapter 6 - Pg 111 "Multiple Choice" 1-10// //Chapter 10 - Pg 192 "Multiple Choice" 1-10// Wednesday, November 11 Homework
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//Chapter 6 - Pg 108 "Review Questions"// 12-15 Possible Controlled Experiment Ideas Monday, November 9 Homework //Chapter 6 - Pg 108 "Review Questions"// 6-10 6) A car is lifted a certain distance in a service station and therefore has potential energy relative to the floor. If it were lifted twice as high, how much potential energy would it have? Twice as much potential energy, if the wire snaps, and the car drops, twice as much potential energy will impact the collision force.
 * Question 12: Can a machine multiply input force? Input distance? Input energy? (If your three answers are the same, seek help, because the last question is especially important.) a) Yes, a good example would be the lever. b) Yes, if the machine is designed so that more force is required but the distance multiplies. An example would be moving the fulcrum of a lever closer to the end being pushed down (the empty end). c) No, the energy put into the machine will come out the same amount, but probably in a converted state; energy cannot be created nor destroyed.
 * Question 13: If a machine multiplies force by a factor of four, what other quantity is diminished, and how much? The distance will decreased, it'll be one fourth of it's original quantity before the force gets multiplied. The input and output energy has to be balanced as energy cannot be created or destroyed. In order for it to be balanced, the distance quantity has to be divided.
 * Question 14: What is the efficiency of a machine that miraculously converts all input energy to useful output energy? 100%, nothing goes to waste, all the energy that comes out is converted and used.
 * Question 15: Is a machine physically possible that has an efficiency greater than 100%? Energy cannot be created nor destroyed, no. A efficiency higher than 100% means that more output energy comes out than the input energy that comes in. This goes against the law stated above, energy cannot be created nor destroyed, but it can be converted. It's like putting in 100 N of force but the work achieved is equal to 1000 N, the energy can't come from mid air (except for gravity).
 * 1) Measure loudness of speaker when pitch of music is altered
 * 2) Measure loudness of speaker when speed of music is altered
 * 3) Generator Vs Motor?

7) Two cars are lifted to the same elevation in a service station. If one car is twice as massive as the other, how do their potential energies compare? The car with twice as much mass will have bigger potential energy because weight is involved in this case.

8) How many joules of potential energy does a 1N book gain when it is elevated 4m? When it is elevated 8m? a) 4 joules because 4 multiplied by 1 is 4 (force multiplied by distance. b) 8 joules because 8 multiplied by 1 is 8 (force multiplied by distance)

9) A moving car has kinetic energy. If it speeds up until it is going four times as fast, how much kinetic energy does it have in comparison? The kinetic energy is 16 times as much, because in the equation, speed is squared. If the unit for the car's starting rate is one, and four times is four, one squared is one while four squared is 16. 16 is 16 times larger than 1; the kinetic energy is about 16 times larger.

10) Compared to some original speed, how much work must the brakes of a car supply to stop a car moving three times as fast? How will the stopping distance compare? The same force is required to stop a moving car moving at three times regular speed; force provided by the brakes, it just requires more work. The car moves three times as fast, to fine kinetic energy, the speed has to be squared, 3 squared is 9; the car's stopping distance will be 9 times further as there is more kinetic energy in the car moving 3 times normal speed. It takes more work to stop this car using the same energy (friction) provided by the brakes. Wednesday, November 4 Homework //Chapter 6 - Pg 108 "Review Questions"// 1-5 1) Cite an example in which force is exerted on an object without doing work on the object.Pushing a box against a wall.

2) Which requires more work - lifting a 50-kg sack a vertical distance of 2m or lifting a 25-kg sack a vertical distance of 4m? The same

3) If both sacks in question two are lifted at the same time, how does the power required for each compare? How about for the case in which the lighter sack is move its distance in half the time? a) Power stays the same because same amount of work is done, and at the same time. b) Power for lighter sack is two times more because same amount of work done in half the time.

4) Exactly what is that a body having energy is capable of doing? A body that has energy is capable of doing work.

5) What are two main forms of mechanical energy? Potential energy and kinetic energy.

Monday, November 2 Homework //Chapter 10 - Pg 191 "Think and Explain" 3, 6, and 13//
 * Question 3: In an electrical force, electrons move.
 * Question 6: 25 N
 * Question 13: A motor uses electrical energy (converting it into usable energy, a generator converts energy into electrical energy, or something else.

5 Scientific Questions 1) Why do opposites attract? What causes them to do so? 2) How are Amperes, volts, and Ohms related and different? 3) How can you tell if an object is charged? 4) Is it possible to create or destroy electrons? 5) Why do opposites attract? What causes them to do so?

Class Work, Thursday September 10, 2009 2. The race car driver rounded the curve at a constant velocity of 100 km/h is wrong because velocity is the same speed and direction of an object. If the car is going around a corner, it is not going in the same direction, so it is not the same velocity.

4. If a huge bear was chasing me and I ran in a zigzag pattern, the bear's mass would work to my advantage because the bear would have to change its velocity every couple of seconds and the bear would not be able to do this for a long period of time, thus, letting me escape.

9. When a car moves along the highway at a constant velocity, the net force on it is zero. You have to have to keep your motor running, because you have to keep the constant velocity to have the net force of zero on it.

13. The weight of the scaffold is 150N, because 250N plus 150N is 400N, which is the whole weight of the scaffold and the man.

19. If you toss a coin straight upward while riding on the train, the coin lands right back in your hand when the train is going along a straight-line track. This is because of the inertia and it keeps the coin with you. Same thing happens when the train is turning. When the train slows down, the coin flies forward, because the inertia of the coin is moving forward.

1. A 2. B 3. C 4. B 5. D 6. C 7. A 8. A 9. D 10. C

2. It hurts to bang against a wall when your carrying a heavy load because the heavy load makes you hit the wall harder, causing more pain. Newton’s Firsr law is most applicable here.

3. When a car is crushed into a compact cube, the mass and weight stay the same because all you do is make it smaller, you don't take any parts away from it. The volume changes because its from a big car to a smaller and easier to move cube.

5. The force of the friction would be 1N, because every action has an opposite reaction.

8. The basketball filled with the rocks would accelerate faster because of the formula a = F/m. The mass of the ball filled with rocks is greater, so it accelerates faster.

9. The force of gravity is stronger than the air resistance, because you slowly drift down, instead of staying in the same place.

13. The terminal speed of the parachutist before opening the parachute is much greater than the terminal speed when the parachute is out. This is because the surface area increases.

14. The gravitational force on a falling body before it reaches terminal velocity is less than when the body reaches the terminal velocity.

1. A 2. C 3. B 4. B 5. D 6. A 7. A 8. A 9. A 10. B

Thursday, September 3rd 2009
The heavier our car is, the more inertia it has and the more friction it has. With more friction and inertia, the motor needs to be more powerful to move the car. This is why a lot of the cars don't move very fast, because the motor is struggling to fight against inertia and friction.

Tuesday, September 1st 2009
We can estimate our car's acceleration by using the data we collected because we can use the acceleration formula. We find out the change of velocity and how long it took to cover the one meter, divide, and then we have the acceleration.

Monday, August 31st 2009
Page 36: # 14-16

14) The reading on the right scale would be 350 N. This is because the upward tension is equal to the sum of the scaffold plus the two painters. This makes the net force of the scaffold zero, giving it the name mechanical equilibrium.

15) The readings of the scale should be half her original weight. Meaning that if you multiply the scales' reading by two, you get Nellie's weight. This method works because of the downward force of Nellie's weight, and the tension from both strings to hold her up.

16) The rope doesn't break because his original weight is divided by two, because there are two ropes that hold him. His weight divided by two is 250 N, which is under 300 N, so the rope doesn't break. But when he tied his rope to the flag pole, the rope had to hold his 500 N weight, not the usual 250 N, this caused the rope to break, Harry to fall into an early vacation.

Sunday, August 30th 2009
Page 35: #4,6 and 7

4) If a huge bear was chasing me and I ran in a zigzag pattern, the bear's mass would work to my advantage because the bear would have to change its velocity every couple of seconds and the bear would not be able to do this for a long period of time, thus, letting me escape.

6) If a ball is at rest in the middle of a toy wagon and when the wagon is pulled forward, the ball rolls against the back of the wagon. This is explained by Newton's first law because the balls inertia tries to keep the ball in one place, but because the wagon is moving forward, the ball rolls to the back of the wagon.

7) You lurch forward in a bus that suddenly slows because your inertia is moving forward, and when the bus stops, your inertia tries to keep moving forwards. You lurch backwards when the bus suddenly picks up speed because your inertia is where you were sitting still, and when the bus lurched forward, and went backwards. This is an example of Newton's first law.