Newton’s Laws of Motion - Answer Key

Newton’s Laws of Motion 1. Who is Isaac Newton? 2. What did Newton discover “under the tree? 3. Who is Galileo Galilei? 4. Which of these scientists was older? 5. Name and Describe Newton’s FIRST Law. 6. Which has more inertia: a heavy ball or a light ball rolling in the same speed in the same direction? 7. Why is Newton’s first law difficult to understand? 8. Name and explain what is not stated in Newton’s first law that plays an important role in motion. 9. What would happen to a baseball if you could throw it in outer space? Explain in terms of inertia and friction. 10. Explain how a car is designed to reduce friction. 11. Explain how a car is designed to increase friction. 12. Explain what is meant by balanced forces. 13. A car travels along a straight road at a steady 40MPH. Are the forces on the car balanced or unbalanced? 14. Name and Explain Newton’s SECOND Law. 15. Can a light object that was hit with a small force accelerate rapidly as a heavier object hit with a big force? Why or why not? 16. Explain what is meant by unbalanced forces. 17. Explain Newton’s THIRD Law. 18. If you hold a backpack in you hand, the force of gravity pulls it downward. What force keeps it from falling to the ground? Answers Newton’s Laws of Motion 1.Who is Isaac Newton? A British scientist who made important discoveries about light, motion and gravity 2.What did Newton discover “under the tree? He realized that there is a gravitational force that constantly pulls objects toward the center of Earth. This forces makes objects fall toward Earth if no other force is there to hold them up. 3. Who is Galileo Galilei? An Italian scientist who lived from 1564-1642. He began to think about motion in a new way. 4. Which of these scientists was older? Galileo was older. (Newton was born the year Galileo died. 5. Name and Describe Newton’s FIRST Law. The Law of Inertia. Describes an object’s resistance to changing its motion and its tendency to keep doing whatever it is doing. An object’s motion cannot change unless a force acts on the object. A change in motion can be a change in an object’s speed, direction, or both. It takes a force to overcome an object’s inertia and to make an object go faster, slower, or change direction. 6. Which has more inertia: a heavy ball or a light ball rolling in the same speed in the same direction? The heavier one because it would take more force to change its motion than the light one. 7. Why is Newton’s first law difficult to understand? The difficulty is that this law also says that no force is needed to keep something moving. Something moving at a certain speed will keep moving at that speed forever unless something pulls or pushes on it. This idea also applies to an object that is not in motion and will remain motionless until a force acts on it. This law contradicts everyday experience because of friction. 8. Name and explain what is not stated in Newton’s first law that plays an important role in motion. Friction is how we explain Newton’s first law. Friction is a force that exists at the boundary between any two pieces of matter that are in contact with each other. Friction is a force that opposes the motion of an object. 9. What would happen to a baseball if you could throw it in outer space? Explain in terms of inertia and friction. A baseball, if thrown in outer space, would continue to move in a straight line at a constant speed forever or until it encounters a force that changes its motion. 10. Explain how a car is designed to reduce friction. Shapes of cars are streamlined to reduce air friction, and oil and grease reduce friction between moving parts. . 11. Explain how a car is designed to increase friction. Tires need to have friction so that they can “grab” the road and brakes need a lot of friction to make the wheels stop turning. 12. Explain what is meant by balanced forces. When the net force is zero, there are balanced forces and there is no change in motion. To achieve a net force of zero means that an applied force balances the force of friction so that the combined force acting on the object is zero. (Ex. Tug-of-War, when there is a deadlock and no one is able to move the other over 13. A car travels along a straight road at a steady 40MPH. Are the forces on the car balanced or unbalanced? The forces are balanced. The frictional forces within the car and from the road are balanced by the equal but opposite force applied by the engine. The net force is zero, and the car travels with constant speed and direction. 14. Name and Explain Newton’s SECOND Law. The relationship between force, mass and acceleration F=ma 1. To equally change the motion of two objects of different mass, more force must be applied to the more massive object. (ex. A wheelbarrow filled with dirt will be much heavier to push than an empty wheelbarrow.) 2. The bigger the force that is applied to an object, the greater the resulting acceleration. (ex. Tap a soccer ball and it won’t go far. Kick the soccer ball and it will accelerate much more.) 15. Can a light object that was hit with a small force accelerate rapidly as a heavier object hit with a big force? Why or why not? Yes, because the ratio of force to mass could be the same for the two situations. For example, the acceleration of 400N/100kg is the same as 4N/1kg. 16. Explain what is meant by unbalanced forces. If net force on an object is not zero, the forces are unbalanced and the object accelerates. Even a tiny force will cause an object to speed up if it is not balanced by another force. 17. Explain Newton’s THIRD Law. The law of Action-Reaction. When one object applies a force on a second object, the second object applies the same size force in the opposite direction, and for the same amount of time, on the first object. (Ex. A launching rocket is propelled (lifted off the ground) because, at the same time as the rocket is pushing the gases down, the force of the gases is pushing the rocket up.) 18. If you hold a backpack in you hand, the force of gravity pulls it downward. What force keeps it from falling to the ground? The “reaction” force is your hand that applies an equal and opposite force on the backpack. However, it is impossible to say which of the two forces is the “action” and which is the “reaction” since they are applied simultaneously. What are Newton's Laws of Motion? ● First--Inertia (see above for this law in detail) The tendency of an object to continue moving at the same speed and in the same direction. Also, its the tendency of an object at rest to remain at rest. ● Second--Relationship between force, mass and acceleration F=ma (Force = mass X acceleration) An increase in mass or acceleration will increase the amount of force. needed to move the object or stop the object. When two objects are in motion, more force will be needed to stop the more massive object. The bigger the force that is applied to an object, the greater the resulting acceleration. ● Third--Action-Reaction with Two Objects For every action there is an equal and opposite reaction. When one object applies a force on a second object, the second object applies the same size force in the opposite direction, and for the same amount of time, on the first object.