Friction is due to surface bumps and also to the stickiness of atoms on the

# Friction is due to surface bumps and also to the

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Friction is due to surface bumps and also to the stickiness of atoms on the surfaces of the two materials. The Force of Friction CHECK YOUR UNDERSTANDING The force of friction can occur A. with sliding objects. B. in water. C. in air. D. all of the above The Force of Friction CHECK YOUR ANSWER The force of friction can occur A. with sliding objects. B. in water. C. in air. D. all of the above Comment: Friction can also occur for objects at rest. If you push horizontally on your book and it doesn't move, then friction between the book and the table is equal and opposite to your push. The Force of Friction CHECK YOUR UNDERSTANDING When Nellie pushes a crate across a factory floor at constant speed, the force of friction between the crate and the floor is A. less than Nellie's push. B. equal to Nellie's push. C. equal and opposite to Nellie's push. D. greater than Nellie's push. The Force of Friction CHECK YOUR ANSWER When Nellie pushes a crate across a factory floor at constant speed, the force of friction between the crate and the floor is A. less than Nellie's push. B. equal to Nellie's push. C. equal and opposite to Nellie's push. D. greater than Nellie's push. The Force of Friction CHECK YOUR UNDERSTANDING When Nellie pushes a crate across a factory floor at an increasing speed , the amount of friction between the crate and the floor is A. less than Nellie's push. B. equal to Nellie's push. C. equal and opposite to Nellie's push. D. greater than Nellie's push. The Force of Friction CHECK YOUR ANSWER When Nellie pushes a crate across a factory floor at an increasing speed , the amount of friction between the crate and the floor is A. less than Nellie's push. B. equal to Nellie's push. C. equal and opposite to Nellie's push. D. greater than Nellie's push. Explanation: The increasing speed indicates a net force greater than zero. The crate is not in equilibrium. distance covered travel time Speed and Velocity Speed is the distance covered per amount of travel time. Equation for speed: Speed = Average speed is the total distance traveled divided by the time of travel. Equation for average speed: Average speed = Instantaneous speed is the speed at any instant of time. total distance covered travel time Speed and Velocity Speed and Velocity CHECK YOUR UNDERSTANDING The average speed in driving 30 km in 1 hour is the same as the average speed in driving A. 30 km in 1/2 hour. B. 30 km in 2 hours. C. 60 km in 1/2 hour. D. 60 km in 2 hours. Speed and Velocity CHECK YOUR ANSWER The average speed in driving 30 km in 1 hour is the same as the average speed in driving A. 30 km in 1/2 hour. B. 30 km in 2 hours. C. 60 km in 1/2 hour. D. 60 km in 2 hours. change of velocity time interval Acceleration Acceleration is the rate at which velocity changes with time. The change in velocity may be in magnitude, in direction, or both.  #### You've reached the end of your free preview.

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• Spring '14
• AnnM.Robinson
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