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# Vertical force on horizontally moving block watch

1. if a block is moving at a uniform velocity along a horizontal line why does it come to stop when I exert a vertical (downward) force on it? surely the normal force will just increase and the net force on the block will be zero (e.g: when a block is sliding and i push my finger down on the block it will stop?)
2. Maximum friction (the friction between two objects which are sliding past each other) is proportional to the normal force. So you push down, the normal force increases, friction increases whilst the driving force does not, the block decelerates and stops.
3. F = uR where f is frictional force, r is normal or reaction force and u is coefficient of friction. Increasing R will increase F Which apposes motion. If the surface was smooth, theoretically there would be no change as u would equal 0

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Updated: January 2, 2013
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