Journal 12/18

1. Why does Jon draw two force diagrams? Does he need two force diagrams to answer this question?

Jon does need to force diagrams to figure out this problem because he must figure out the force of Chris on the ball with the ball as the object of interest so that he could figure out the force of the ball on chris when chris is the object of interest.

2. Will the calculation in the box produce the correct answer for the mass of Chris? How do you know?

When I calculated out the mass of Chris, I dot 173.5 kg, not 196 kg.

3. What mistake (or mistakes) can you find in this work? What effect does each mistake have on the solution, if any? What does Jon need to understand in order to fix the mistake?

I found Chris to weigh 173.5 kg because Jon divided by the force of the gravitational pull, not taking into account that acceleration is equal to Fnet over mass. In order to find the mass, you have to subrract the 8 kg of the ball from the mass and set the mass equal to x and solve it out that way.

Journal 12/11

1. How do we know that the force of the string on the bob does not become zero when it is moving?

Ryan makes four force diagrams because there are four instances in which forces are being exerted. Both when the cart is held and let go and when the bob is moving and at rest. The differences between Ryan's diagrams and mine were that his arrow lengths were different then mine, because when i did this on my own, i thought the force of the string on the bob while it was moving would be at zero, now however, i know that this is not true because if there is a force being exerted on an object, it will always exert a force on that object. Meaning that because in a previous diagram the string and the bob had a force diagram, then the would still have it while the bob was moving.

4. Explain how you know the force of the string on the bob has decreased but is not zero. Your answer is not convincing. A good explanation will involve the cart.
Started late and not yet complete. Follow instructions to complete the assignment and earn 3/4 credit. Grade = 1/4

You know the the force of the string on the bob has decreased, but is not 0 because the cart is being pulled by the string connected to the bob and we know that because of Newton's second law objects will always exert the same amount of force on one another so long as they are touching.

Journal 12/18

1. Why does Jon draw two force diagrams? Does he need two force diagrams to answer this question?

Jon draws two force diagrams because he is solving for Chris' mass. However, he could have only drawn one diagram using Chris as the object of interest because he did nothing with the information found when the ball was the object of interest.

2. Will the calculation in the box produce the correct answer for the mass of Chris? How do you know?

If Chris' mass is 196 kg then yes it works out. The answer sounds reasonable and the reason i know this is because i checked math out with a calculator.

3. What mistake (or mistakes) can you find in this work? What effect does each mistake have on the solution, if any? What does Jon need to understand in order to fix the mistake?

I'm pretty sure that there are not any mistakes on Jon's work.

1. How do we know that the force of the string on the bob does not become zero when it is moving?

Ryan makes four force diagrams because there are four instances in which forces are being exerted. Both when the cart is held and let go and when the bob is moving and at rest. The differences between Ryan's diagrams and mine were that his arrow lengths were different then mine, because when i did this on my own, i thought the force of the string on the bob while it was moving would be at zero, now however, i know that this is not true because if there is a force being exerted on an object, it will always exert a force on that object. Meaning that because in a previous diagram the string and the bob had a force diagram, then the would still have it while the bob was moving.

4. Explain how you know the force of the string on the bob has decreased but is not zero. Your answer is not convincing. A good explanation will involve the cart.
Started late and not yet complete. Follow instructions to complete the assignment and earn 3/4 credit. Grade = 1/4

You know the the force of the string on the bob has decreased, but is not 0 because the cart is being pulled by the string connected to the bob and we know that because of Newton's second law objects will always exert the same amount of force on one another so long as they are touching.

Homework 12/17

How does exerting a force which is not perfectly horizontal and not perfectly vertical on an object change the way you need to approach a problem like this? What extra steps/precautions do you need to make when solving this problem?

The fact that force is on an angle changes the way that you calculate the Fnet forces. You have to make sure that you calculate the Fnet in the x direction and in the y direction using sine and cosine. You have to be sure that you pay attention to your numbers and the directions and magnitudes of each of the forces in the correct axis.

Journal 11/20

Please explain what is not correct about your answer to 6E.
Started late and not yet complete. Follow instructions to complete the assignment and earn 3/4 credit. Grade = 1/4

6E. Explain the relationship between the direction of the total force exerted on the object of interest and what is happening to the motion of the object of interest.

If there are balanced forces, then there is no movement, however the addition of an unbalanced force means that it is moving.

I know that this is wrong because balanced forces just mean that the object is equilibrium, meaning it could be moving or not. However, if there is and unbalanced force, that means that the object is accelerating in whatever direction the unbalanced force is.

Journal 12/11

1. Why does Ryan make four force diagrams?
2. Describe differences between Ryan's solution and yours. How did your understanding of this problem change after seeing this video?
3. Why did Ryan change the length of the arrow representing the force of the string on the cart?
4. How do we know that the force of the string on the bob does not become zero when it is moving?

Ryan makes four force diagrams because there are four instances in which forces are being exerted. Both when the cart is held and let go and when the bob is moving and at rest. The differences between Ryan's diagrams and mine were that his arrow lengths were different then mine, because when i did this on my own, i thought the force of the string on the bob while it was moving would be at zero, now however, i know that this is not true because if there is a force being exerted on an object, it will always exert a force on that object. Meaning that because in a previous diagram the string and the bob had a force diagram, then the would still have it while the bob was moving.

Journal 11/20

6A. Explain why you don't know whether the ball is moving in the +x or -x direction, or not moving at all.

You can tell what direction the ball is moving. The +x axis is labeled in the direction of the unbalanced force. Therefore you know what direction the ball is moving in.

6B. Explain what would be happening to the motion of this ball if it were moving in the +x direction, with forces exerted on it by other objects as shown.

The stick is pushing the ball in the positive direction.

6C. Explain what would be happening to the motion of this ball if it were NOT moving yet, with forces exerted on it by other objects as shown.

It has to be moving because there is an unbalanced force shown.

6D. Explain what would be happening to the motion of this ball if it were moving in the -x direction with forces exerted on it by other objects as shown.

The stick would have to be pushing the ball in the opposite direction for it to move in the -x direction.

6E. Explain the relationship between the direction of the total force exerted on the object of interest and what is happening to the motion of the object of interest.

If there are balanced forces, then there is no movement, however the addition of an unbalanced force means that it is moving.

Journal 12/4

1. Explain what part of your original work made me think that you did NOT show understanding of Newton's second law: acceleration of an object is proportional to the net force exerted on the object by other objects, and inversely proportional to the mass of the object. the reason you thought i did not show understanding of newton's second law is because, i originally thought that if you doubled the mass you would also double the speed at which it falls. Which is doesn't.

1. Write a mathematical expression for the force that the earth exerts on an object of mass m. Remember that when an object is falling freely Fnet = Fearth on obj

Fnet= mass (9.8 m/s/s)

2. Your friend Abe says "If you drop a marble and a bowling ball from the top of the school, being careful to let go of them both at the same time, they will both hit the ground at the same instant. This means the force of the earth is the same on both objects." Do you agree with Abe? Why or why not? If you disagree, how would you try to convince him using a real-world example that he could try himself?

The force of the earth is not the same on both of the objects. A marble has a different mass than a bowling ball. While both will hit the ground at the same time, the force of the earth on the bowling ball is greater than the force of the earth on the marble. This is due to the fact that the force of the Earth on any object is equal to the mass times the 9.8 constant. If you drop two weights, they fall at the same time, and land together, but the force is much greater on the one weight with more mass. The more mass an object has, the more force the earth exerts on it.

3. Your friend Ben says "If I duct-tape two bricks together the earth pulls on them twice as hard as a single brick. Therefore, the double brick will fall twice as fast." Do you agree with Ben? Why or why not? If you disagree, how would you try to convince him using a real-world example that he could try himself?

Ben is partially true. If you tape two bricks together, then they the earth will pull on them twice as much because you are doubling the mass of the object. However it will not fall any faster because all things fall at the same speed. You can see this because when you drop two objects with two different masses, they land at the same time.

2. Answer the original questions carefully now that you understand the lesson.

3. What activity, experiment, or lesson helped you to understand this lesson better? The video really helped me to understand the lesson.

Homework 12/7

a) When the Earth exerts a force on the book, the book exerts a force on the earth

b) When a table exerts a force on the book, the book exerts a force on the table.

c) When a tennis racket exerts a force on the ball, the ball exerts a force on the tennis racket

d) When car tires push back on the Earth’s surface, the Earth’s surface pushes back on the car tires.

Journal 12/4

We also know that if we study the motion of any object that is freely falling near the surface of the earth we find that it moves with an acceleration of 9.8 m/s/s (if its interaction with the air is small enough to ignore.)

Make a new post on your blog titled "Journal 12/4" and address the following questions:

1. Write a mathematical expression for the force that the earth exerts on an object of mass m. Remember that when an object is falling freely Fnet = Fearth on obj

Fnet= mass (9.8 m/s/s)

2. Your friend Abe says "If you drop a marble and a bowling ball from the top of the school, being careful to let go of them both at the same time, they will both hit the ground at the same instant. This means the force of the earth is the same on both objects." Do you agree with Abe? Why or why not? If you disagree, how would you try to convince him using a real-world example that he could try himself?

Here's the thing, the force is not the same. The equation to find the earth's Force is mass x 9.8 m/s/s. So the bowling ball has a greater force pull than the marble because the marble has less mass. A feather and a pair of glasses have two different masses so their forces would not be the same.

3. Your friend Ben says "If I duct-tape two bricks together the earth pulls on them twice as hard as a single brick. Therefore, the double brick will fall twice as fast." Do you agree with Ben? Why or why not? If you disagree, how would you try to convince him using a real-world example that he could try himself?

Ben's right, the mass is increased by two, so the force will be twice as much as if it was just one. Therefore the mass will be greater and it will fall faster.