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Determine the exact amount of tension for the Horizontal Atwood Machine.

Determine the exact amount of tension for the Horizontal Atwood Machine. N. We are going to compare the tension to the amount of mass required to cause an equivalent gravitational force. (The tension is not equal to a weight!!). T. M. y. x. W M. M = 875 g m = 200 g. T. y. m. x.

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Determine the exact amount of tension for the Horizontal Atwood Machine.

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  1. Determine the exact amount of tension for the Horizontal Atwood Machine. N We are going to compare the tension to the amount of mass required to cause an equivalent gravitational force. (The tension is not equal to a weight!!) T M y x WM M = 875 g m = 200 g T y m x For M: Wm For m:

  2. Friction What is friction? • Resistance to the motion of an object due to contact with its surroundings. • It is caused by microscopic interactions between the two interacting surfaces. • E.g.: Dry friction – between two solid surfaces. • Fluid friction – between a solid and a fluid or two fluids. • - This is more commonly called Drag. Microscopic view of interaction between two surfaces resulting in a frictional force. There are two different circumstances for friction we will use: Static friction – friction present when both surfaces are stationary. Kinetic friction – friction present when at least one of the surfaces is moving. fsmax – magnitude of the maximum static frictional force [N] fk – magnitude of the kinetic frictional force [N] ms – static coefficient of friction [dimensionless] mk – kinetic coefficient of friction [dimensionless] N – magnitude of the normal force [N]

  3. Typically ms > mk and depends on the materials involved. Typical range 0.03 < m < 1.0, but m is not limited to this range. The frictional force is always parallel to the interacting surfaces and opposite to the direction of motion. The frictional force does not depend on surface contact area! The expression for the static frictional force can only be determined at the point of impending motion, which corresponds to a maximum value. For applied forces less than the maximum static frictional force the object will not move and therefore fs = F. For applied forces greater than the maximum static frictional force the object will move and therefore we will consider kinetic friction. This plot is more typical of how we approach the transition from the static region to the kinetic region.

  4. A person pulls a box across the floor. Which is the correct analysis of the situation? The box moves forward because the person pulls forward slightly harder on the box than the box pulls backward on the person. 2. Because action always equals reaction, the person cannot pull the box- the box pulls backward just as hard as the person pulls forward, so there is no motion. 3. The person gets the box to move by giving it a tug during which the force on the box is momentarily greater than the force exerted by the box on the person. 4. The person’s force on the box is as strong as the force of the box on the person, but the frictional force on the person is forward and large while the backward frictional force on the box is small. 5. The person can pull the box forward only if he or she weighs more than the box.

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