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Chapter 12 Guided Reading – This information will be your notes for Chapter 12. Make sure that you provide as much information as you need to understand what the question was and your complete answer! (Chapter 12 is pages 394 – 429)Section 12.1What is gravity? Why is it considered a universal force? – Gravity is the force that objects exert on each other because of their masses. It is considered a universal force because it acts between any 2 masses anywhere in the universe.What two factors does the force of gravity depend on? Make sure to explain both of these in depth! – Gravity depends on 2 factors – the mass of the objects and the distance between them. The more mass the objects have, the greater the force of gravity the masses exert on each other. If one of the masses was doubled, the force of gravity between the two objects would double as well. As distance between objects increases, the force of gravity decreases. If the distance was doubled, gravity would be ? as strong.What is the acceleration due to gravity on Earth? How can we use this to calculate the force of gravity on an object? – Acceleration due to gravity = 9.8 m/s2; you can use this to calculate the force of gravity on an object by using the formula F = m*aHow does the rate at which objects fall in a vacuum compare with each other? Explain why this happens. – In a vacuum (where there is no air), objects all fall at the same acceleration (9.8 m/s2). Gravity exerts more force on more massive objects, but more massive objects also have more inertia.Explain the difference in weight and mass. – Weight is a measure of the force of gravity on an object; mass is a property that is constant for objects no matter where they are located.Give some examples of how gravity can keep objects in orbit. – Gravity causes planets to orbit the Sun, and the Moon to orbit Earth. It also keeps satellite in orbit around Earth.Section 12.2What is friction and when does it occur? What would happen if there was no friction? – Friction is the force that resists motion between 2 surfaces in contact with each other. If there was no friction, objects would move as soon as you applied a force. If there was no friction, many activities, like walking and driving, would be impossible.What are the 3 factors that determine the amount of friction? Explain each of these in detail and give examples.Type of surfaces – Different surfaces produce different amounts of friction; for example, ice produces much less friction than asphalt, which is why it is harder to drive in the snow.Motion of the surfaces – You need a larger force to start something moving than you do to keep it moving. Friction is lower when an object is moving.Forces pressing the surfaces together – The more force that is pressing surfaces together, the harder it is for the surfaces to slide past each other. When an object is placed on a surface, the weight of the object presses on that surface and the surface exerts an equal and opposite reaction force, determining the amount of friction.Explain how friction can produce heat. Give an example of when the heat caused by friction can create a flame. – Molecules on surfaces move faster, causing the temperature to rise; striking a match on a rough surface produces fire.What is a fluid? – A fluid is a substance that flows easily. (Gases and liquids)Explain how motion through a fluid can produce friction. – When an object moves through a fluid, it pushes the molecules that make up the fluid out of the way and those same molecules exert a reaction force on the object, creating a type of friction called drag.What is air resistance? What factors determine the amount of air resistance? – Friction due to air; surface area of object (larger surface area creates more air resistance) and speed (when speed increases, air resistance increases)Section 12.3What is pressure and what does it describe? – A measure of how much force is acting on a certain area; Pressure describes how concentrated the force isSection 12.4Explain buoyant force. – The upward force on objects in a fluid is buoyant force; this is the reason ice floats in water, and the reason that objects seem lighter when they are in water. Briefly summarize Bernoulli’s Principle. – increase in the speed of the motion of a fluid decreases the pressure within the fluid, so the faster a fluid flows, the less pressure it exerts on surfaces it flows over; airplane wings are shaped so that air flows faster over the top of the wing, causing a lifting force. ................
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