CHAPTER 10 QUESTION SETS ANSWERS

1. What is the definition of force? A force is a push or a pull.

2.In a paragraph of 3-5 sentences, explain your use of forces when you prepared for school today. Include 5 times you used a force, and none may be in the book on page 374. I pushed off my bed and stood on the floor. My feet pushed off the floor to walk downstairs and I picked up my coffee pot, pushed the water faucet to get fresh water and then used force to empty the coffee grounds into the trash. I then waited for the coffee pot to push water through the grounds. I pulled the door open to the backyard so my dogs could push urine out of their bladders!

3.Why is force a vector quantity? A vector quantity has a magnitude and a direction. Forces have both magnitudes (N) and directions (arrows).

4.Explain how arrows help us show forces on paper. First, arrows tell us what direction the force is being applied. We just have to look. Second, they show us magnitude by their length and their width.

5.What is the SI unit for force? If you pick up 3 apples, about how many Newtons of force are you using? The SI unit for force is the NEWTON. One Newton is about equal to the amount of force required to pick up one apple. So, to pick up 3 apples, it would take about 3 Newtons.

6. How do you find out the net force acting on an object? The net force is the amount of force left over when you add up all the forces acting on an object.

7.When would you add forces acting on an object? When would you subtract the forces acting on an object? If the forces are acting in the same direction, you add the forces to make a bigger net force. If the forces are acting in opposite directions, you subtract.

8.If the net force on an object is zero, what happens to the object? If the net force is equal to zero, the object will have no net force, and will not move.

9.How can you tell which direction an object will move if the net force is not zero? You look at the arrows…the direction of the largest arrow determines the overall direction the object will move. The object will move in the same direction as the largest force.

10. Why would the forces acting on the box in the first two pictures on pages be unbalanced? They must be unbalanced, because there is a net force and movement. In the first picture, the box goes to the right with a force of 300N. In the second picture, the box moves to the right but with less force 100N.

11.How are unbalanced forces related to the idea of acceleration from chapter 9? When the forces acting on an object are unbalanced, the object moves. Any change in movement is acceleration.

12. Why is the 3 rd picture of the box on page 377 a good example of balanced forces acting on the box? Balanced forces do not result in acceleration. Both girls are pushing equally hard in opposite directions so their forces are cancelled. There is no net force. The forces on the box are balanced. NO acceleration.

13.Complete question 2c (only) on page 377. Since the forces are in the same direction, you add them. The net force is 270N. No specific direction was written, though.

1.What is friction? Friction is a force that two surfaces exert on each other when they rub against each other.

2.What are the two factors that affect friction? The two factors that affect friction are the types of surfaces and how hard the surfaces push together (the weight).

3.Briefly list the four types of friction. Include the definition and then one example of each as you got ready for school today. No exact book examples! Static friction is between two surfaces that are not moving. Pushing the chair back under the table is an example of static friction before sliding friction. Sliding friction occurs when two surfaces slide over each other. Pulling Sophie, my bullmastiff, across the floor by her front paws is an example of sliding friction! Rolling friction occurs when an object rolls across a surface. When I roller skated to school this morning, I used rolling friction. Fluid friction occurs when a solid object moves through a fluid. When I swam to school today in the ocean, I experienced fluid friction.

4. List the 4 types of friction in order from greatest to least. STATIC, SLIDING, ROLLING, FLUID

Static Friction Picture

5.Is it harder to get a stalled car moving or keep it going once you got it to move? Why? You have to overcome the static friction first and that is the worst one. Once it is moving, static friction is replaced with rolling friction which is a little easier.

6. What is gravity? Gravity is a force that pulls objects toward each other.

7.How do mass and distance affect the gravitational attraction between objects? Between two objects, as the mass of the two objects goes up, so does the gravitational attraction. But, as the distance goes up, the attraction between them goes down.

Gravitational Attraction Picture

8. What makes up your weight? What makes up your mass? My weight is made up of gravity pulling me down and the mass of my body. The atoms and molecules in my body make up my mass.

9. If you weighed 2000 N here on Earth, how much would you weigh on the Moon? (The moon’s acceleration due to gravity is 1/6 th ours.) If you went to the moon, your weight would be 1/6 th of 2000 or N

Weight Mass Picture

10. What is the real definition of Free Fall? Free falling is when the only force affecting a falling object is the force of gravity. So, there would be no air resistance.

11. Estimate the weight in Newtons of the following: a mechanical pencil, a walnut, a bottle of water, a calculator.

12.What would be the velocity of an object in a state of free fall after 4 seconds? V = AT so, V = 9.8 m/s/s X 4 s, V = 39.2 m/s

Obj Fall at same rate pic.

13. How does air resistance affect falling objects? Air resistance slows down falling objects. 14. How does gravity affect a dropped object compared to a thrown object? The objects will hit the ground at exactly the same time. 15. Name two types of elastic matter. A kitchen sponge and a basketball are two types of elastic matter.

gravity tube, grav. Oak tree

16. Describe on example of a compression force in your home…not a couch! My bed is an example of a compression force. 17. Do the same with tension force…not a shoe! Clothes on a clothesline is an example of tension force.

Section 3 Newton’s First and Second L aws due: _____________ 1. Why do you think Newton’s first Law is sometimes called the Law of Inertia? Inertia has to do with the tendency of all objects to keep doing what they are already doing. Newton’s first law says that objects will keep doing what they are already doing unless an unbalanced force acts on them. So, they both have to do with inertia.

2. How are mass and inertia related? The amount of inertia an object has depends on the amount of mass the object has. 3. Using the words force, mass, and acceleration, describe a person rolling a tennis ball down a table. When a person pushes the tennis ball, he applies a force to it. The force must be large enough to move the mass of the ball. As the ball rolls down the table it decelerates due to friction with the table and air resistance.

4.If the mass of an object increases, what happens to its acceleration if the force YOU apply stays the same? If your friend helps you, what happens to the acceleration? If the mass goes up, the same force will have less of an effect and the object will not accelerate as much. If my friend helps me, then the force is doubled, the mass stays the same and the acceleration increases.

5What is the formula for Newton’s Second Law of Motion? The formula is: F = MA

Section 4 Newton’s Third Law due: ____________ 1. What is Newton’s Third Law of Motion? For every action there is an equal and opposite reaction.

2.Right now…look around you and describe one example of action/ reaction pairs. *When you push on your desk, your desk pushes back on you. *When I sit in my chair, the chair pushes up on my fanny and my fanny pushes back on the chair. *Writing on my paper causes me to push on my paper and the paper pushes back on my pencil.

3. Why don’t action reaction pairs cancel so that nothing happens? They do not cancel out because they are acting on different objects.

4. How can you calculate momentum? Momentum is calculated by multiplying the mass of the object times its velocity. Mom = mass X velocity

5.Complete the momentum problems on page 396 in Math Practice. Mom(golf) = m x v Mom= kg x 16 m/s Mom = 0.72 kg-m/s Mom(base) = m x v Mom= 0.14kg x 7m/s Mom = 0.98 kg-m/s

6.Explain conservation of momentum with 2 moving objects, one moving object, and connected objects. (Use page 399 in your book.) A. Two moving objects have a certain amount of momentum. When they collide, the faster one will slow and the other will speed up. The total momentum after the collision is the same. B. One moving and one not moving. After collision, the one not moving will move and the other will slow down. The total momentum stays the same. C. One moving one not but hooked together…both will travel slower than before but the total momentum is the same because the mass went up while the velocity went down.