|Friction arises when two surfaces are rubbed against one another. Friction can be helpful and not so helpful. Here is an axle rotating in a hole in a beam. When the axle rubs against the inside of the hole, that causes friction. The frictional force wants to slow the axle down. That is why when you spin the axle with your hand, it comes to a stop.||
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||Here is a mobile robot turning in place. The friction between the front wheel and the ground prevents the robot from turning smoothly.|
|Different surfaces have different frictional characteristics. Very smooth surfaces, like tiled floors, have low friction, so the robot turns easily. Carpeted floors have much higher friction, so the robot does not turn as easily.||
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||We can use friction to our advantage. Rubber has very high friction. These rubber tires on the gripper increase the friction between the gripper and the object it is trying to pick up. The rubber tires let the gripper hold on to the object better.|
|Friction is used to slow things down. Automobile or bicycle brakes use friction to slow down the rotating wheel.||(There will be a picture here).|