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### 40 Cards in this Set

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 Speed can be measured in units of distance and time, such as _________. kilometers per hour speed a measure of how far something travels in a certain period of time What effect do oil and grease have on friction? The make surfaces slip more easily across each other, reducing friction. The can reduce heat and other damage caused by friction. How can you use distance and time to measure speed? measure the distance and divide it by the time to find the speed The force that pulls objects together is called ________. gravity kilometers per hour the number of kilometers something can travel in one hour mass the amount of matter in an object velocity a measure of speed in a certain direction The rate at which velocity is changing is ________. acceleration How is velocity different from speed? Speed is measure of distance traveled in a certain time; velocity is a measure of speed in a certain direction How does gravity affect the velocity of falling objects? Gravity accelerates the rate at which objects fall; it makes them fall faster as the distance between the earth and objects decreases The friction caused by gas molecules hitting an object is __________. air resistance inertia the tendency of objects to stay in motion or to stay at rest or to remain in motion unless an outside force causes a change Speed in a certain direction is ____________. velocity How do forces work in pairs when a frog jumps off a floating water lily leaf? The frog pushes backward on the leaf (action force) and the leaf pushes forward (reaction force) on the frog . This causes the frog to move forward and the leaf to move backward. Engineers ____objects to reduce friction with gas molecules in the air. streamline weight the force gravity exerts on an object's mass Name two ways to reduce friction and two ways to increase it. Reduce friction-oil, grease, water; streamline, make surface smoother, add wheels. Increase friction-make surface rougher, use brakes How does its mass affect the way an object moves? The greater the mass of an object, the greater the force of gravity between it and another object. The object with less mass will move more because less force is required to maove it. The force that acts to resist motion between two surfaces is ______. friction streamline to design smooth, rounded surfaces on an object so it slips through the air with the least possible How does air resistance affect the way objects move? Air resistance pulls on objects, slowing them down. air resistance friction caused by gas molecules in the air hitting an object and slowing it down An object's ______ it its tendency to continue moving or to remain at rest. inertia How does the distance between two objects affect the way they move? The farther apart two objects are, the less the attraction between them. The amount of matter that makes up an object is its _____. mass What is needed to overcome inertia? A force is needed to overcome an object's inertia. To find your _____, divide the distance you travel by the time it takes. speed When might you want to decrease friction? when moving heavy objects, to aid machine with moving parts, and so on The force gravity exerts on an object's mass is its ______. weight friction a force that resists the movement of one surface past another surface What types of surfaces produce greater friction? Rough, bumpy surfaces such as carpet, sandpaper, and grass produce more friction than smooth surfaces. If you shoot an arrow into the air, why doesn't its inertia just keep it going in the same direction? Gravity caused by the erath's mass eventually pulls the arrow toward the ground. acceleration rate of change in speed or direction of movement Gravity a force that acts to pull pairs of objects together When might you want to increase friction? to prevent slipping on ice, or applying brakes What types of surfaces produce the least friction? Smooth, slippery, icy, or waxed surfaces produce less friction than rough surfaces. How do seat belts relate to inertia? Seat belts help prevent people from continuing to move forward when a vehicle stops quickly. Name a way to cause a change in velocity slow down, speed up or change direction How does friction affect the way objeact move? Friction slows the movements of objects