Physical Science



Name: ______________________________Physical ScienceNewton’s Laws Study GuideHonor Students: In addition to the information in this study guide, you are responsible for answering questions about the following: terminal velocity, free fall, and calculations of Newton’s 2nd law with conversions.What is the speed of an object?A measure of how fast the object is movingWhat is the velocity of an object?A measure of how fast AND in what direction the object is movingWhen is an object accelerating?When the object is changing direction, speeding up, or slowing downWhat would happen if you dropped a golf ball and a bowling ball off the top of a building? Which would land first? They would both hit the ground at the same time.The acceleration due to gravity is the same for all objects. Explain this statement. Draw a picture to show an example of this.All objects accelerate (change speed) as they move toward the ground) at the same rate. They go faster every second – always the same amount of “faster”. INCLUDEPICTURE "" \* MERGEFORMATINET What is the rate of acceleration for all objects, due to gravitational pull? What does this number mean?The rate of acceleration due to gravity is 9.8 m/s/s. This means that after the first second of falling, an object is going 9.8 meters per second. But, since it increases by 9.8 m/s every second, after second #2, the object is falling at 19.6 meters per second. After the third second, the object is speeding downward at 29.4 m/s. If all objects fall to the earth at the same rate of acceleration due to gravity, why does a feather drop more slowly?Because the feather is not very massive and is very flat. It has a lot of surface area. Because of this shape, the friction from the air particles it hits on the way down slow it down. Other examples of things that drop more slowly are flat pieces of paper and leaves.What is Newton’s First Law of Motion? Tell what it means in your own words.“An object at rest remains at rest and an object in motion remains in motion at a constant speed and in a straight line, unless acted on by an unbalanced force.” In other words, if an object is still (not moving), an unbalanced force is necessary to make it move. Once an object is moving, it will go in the same direction and at the same speed, unless some new force stops it, slows it down, or changes its direction.The first part of Newton’s First Law talks about objects at rest remaining at rest. Are the forces on these objects balanced or unbalanced?Balanced; there is no motion.The second part of Newton’s First Law talks about objects in motion remaining in motion unless other forces act on it. Are moving objects experiencing balanced forces or unbalanced forces?Unbalanced. We know, because the objects are already moving, and unbalanced forces produce movement.What is the primary force that works against motion?Friction is the primary force that works against motion.Describe a circumstance where you want friction to work against Newton’s First Law. (Note: I said DESCRIBE. One or two words is not a description.)Example: If I was riding my bicycle, and there was no friction to work against Newton’s First Law, I’d give a first push, and I would never be able to turn or stop. The friction of my hand against the handlebars, and the tire against the pavement, allows me to make turns – Newton’s Law wants me to go straight! The sliding friction of the brakes allows me to stop – Newton’s Law wants me to keep going!Newton’s First Law also has another name. What is it?The Law of Inertia. (Memory trick: “I” is the Roman numeral for one, so remember Newton’s Law #1 is inertia, that starts with an “I” – capital “i”).Copy Newton’s Second Law here:“The acceleration of an object depends on the mass of the object, and the amount of force applied to the object.”Now rewrite the law in your own words.How fast something accelerates depends on two things: the mass of the object and how much force was put on it to make it move. The less massive the object, the faster it will tend to accelerate. Also, it a lot of force was put on it to make it start moving, then it will tend to go faster. We know this from our real life experiences. If you pushed these two grocery carts with the same amount of force, which would accelerate faster? Explain this using Newton’s Second Law.The empty grocery cart will accelerate more rapidly, because it has less mass. Newton’s Second Law says that how quickly something accelerates depends on its mass, and the force put on it. If the force is the same for both, then the empty cart will move more quickly. INCLUDEPICTURE "" \* MERGEFORMATINET INCLUDEPICTURE "" \* MERGEFORMATINET Which will accelerate faster, shopping cart “A” which is pushed with a force of 10 N or shopping cart “B” which is pushed with a force of 30 N? Mass = 10kg Mass = 10kg Shopping cart “B” will accelerate more rapidly, because it was pushed with more force. Newton’s Second Law says that how quickly something accelerates depends on its mass and the force put on it. If the mass is the same for both, then the cart pushed with more force will move more quickly. INCLUDEPICTURE "" \* MERGEFORMATINET INCLUDEPICTURE "" \* MERGEFORMATINET A BYou will use the following formulas for the next two questions:a = F/mF = m times aIf an object has a mass of 20 kg and has a force of 100 N exerted on it, what would be its acceleration? Show your work, including which formula you used!!!a = F/m a = 100 N divided by 20 kgacceleration = 5 m/s/sIf an object has a mass of 2.5 kg and is accelerating at 4 m/s/s, what would be the force on the object? Show your work, including which formula you used!!!F = m times aF = 2.5 kgtimes 4 m/s/sF = 10 NName two ways to increase the acceleration of an object.You can increase the acceleration of an object by taking away mass (make it less massive, like emptying a grocery cart, or a box) or by increasing the force you put on it.Copy Newton’s Third Law.“Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first.”Rewrite Newton’s Third Law in your own words.When you put a force on something there is always another force that goes with it. That other force has the same strength (equal amount) but goes in the opposite direction. What is a “force pairs”? Give an example.When one force is exerted, another force always happens – equal, but in the opposite direction. So, when I sit on a chair, I exert a force on the chair, equal to my weight, and in a downward direction. The chair is also exerting a force on me. It pushes me up (opposite direction) and has a force that is equal to my weight (otherwise, it would break!). Explain the action of jumping on a trampoline in terms of Newton’s Third Law. Explain what happens to you if you jump harder, using Newton’s Second Law. Draw a sketch to help you. Newton’s Law says when a force is applied to an object, there is an equal force applied from the object, in the other direction. When you jump on a trampoline, you apply force to the trampoline, and the trampoline applies a force to you. These are the force pairs described in Newton’s Third Law. If you jump harder, you are increasing the force, so you will accelerate more quickly, according to Newton’s Second Law.The trampoline applies a force to you – a push upward!You apply a force to the trampoline – a push downward. INCLUDEPICTURE "" \* MERGEFORMATINET 25. Using the example of the trampoline above, explain what happens to you if you jump harder, according to Newton’s Second Law. Draw new force arrows to illustrate this. You are jumping higher because you hit the trampoline with a greater force, the trampoline will hit you back with that same amount of force – Newton’s 3rd law!If you jump harder, you are applying more FORCE to the trampoline. Newton’s 2nd law says that if you apply more force, you will have a greater acceleration. You will be jumping both higher and faster. INCLUDEPICTURE "" \* MERGEFORMATINET What would happen if someone who was less massive jumped on the trampoline. Would they need to use more force, or less force, to get the same acceleration as the person in question 31. (Hint: use the formula for Newton’s Second Law and make up some numbers for the people’s masses to check out your prediction.)The girl on the left has less mass than the girl on the right. INCLUDEPICTURE "" \* MERGEFORMATINET INCLUDEPICTURE "" \* MERGEFORMATINET less mass more massWe can use this formula to see what happens if to the acceleration if the girls apply different amounts of force: force = mass time accelerationLet’s say that the girl on the left has a mass of 40kg and the girl on the right has a mass of 50 kg. We say we want them to have the same acceleration… so let’s say we want them to have an acceleration of 2 m/s/s (every second, the girls’ speed would increase by 2 m/s).Let’s plug in the numbers: INCLUDEPICTURE "" \* MERGEFORMATINET INCLUDEPICTURE "" \* MERGEFORMATINET F = (m)(a) F = (m) (a) F = (40 kg) (2 m/s/s)F = (50 kg) (2 m/s/s) F = 80 N F = 100 NSo, it takes MORE force for the girl with more mass to have the same acceleration as the girl who has less mass.What is momentum?Momentum is how hard an object is to stop, once it starts moving. Momentum depends on an object’s mass and velocity. The more massive an object, the more momentum it has. The higher the velocity, the more momentum the object has. Momentum = mass x velocityWhen we throw a bowling ball, we can make the pins fall down (assuming we are good at it, or the bumpers are up!). Explain what is happening, using the term momentum. Draw a sketch to help.When we throw the bowling ball, we cause it to move (unbalanced force). If the bowling ball is massive, and it has a lot of velocity, it can have a lot of momentum. This means it is hard to stop. When it hits the pins, because it has so much momentum, it knocks lots of them over. Bowling balls that are less massive don’t have as much momentum. Also, if they are going slowly, they don’t have as much momentum. So, the goal is to throw a heavy ball fast – and accurately, of course! INCLUDEPICTURE "" \* MERGEFORMATINET lots of momentum lots of force means means the ball is hard to stop – it the ball will go fast takes lots of pins to stop it! Which has more momentum, a mouse running at 1 m/s north or an elephant walking at 3 m/s east? Explain your answer.An elephant walking at 3 m/s will have more momentum, because it is more massive and it is going faster. ................
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