Friction

Write your FULL name and class section Friction1 What is the difference between socks and sneakers? Okay - there are a lot of differences, but one difference is that sneakers have a lot more friction than socks. In your socks, you can get a running start and slide a long way down the hall. In your sneakers, you can get a running start and . . . stick to the floor!2 Friction is the force that happens when two things rub together. The effect of friction is usually to slow you down. With less friction, you can move more easily. With more friction, you have to work harder to move the same distance, because the friction slows you down.3 Friction can be useful. Sometimes you want sneakers that grip the floor. The friction caused by the soles of your sneakers is good for running track and for playing basketball. Friction is very useful on items such as snow tires.4 Friction can also get in the way. Often it is the force that people are trying to overcome. If you think about the different ways that people have traveled, you will see that anything that reduces friction makes travel easier and faster. Wheels reduce a vehicle's contact with the ground and thereby reduce friction. A smooth surface produces less friction than a rough one, such as smooth racecar tires, for example. Oil is used to reduce friction in a vehicle's engine. Ball bearings reduce friction, too.5 Another way that people try to travel with less friction is by not traveling on the ground at all. Boats avoid the friction of traveling on the ground, but they have their own friction to deal with because contact with water causes another type of friction called fluid friction. The fastest boats ride high in the water; the less contact with the water, the less friction. Airplanes and helicopters avoid the friction of land travel too, but they have drag, another form of friction, and gravity to fight.6 One of the newest kinds of transportation built to avoid friction is the maglev train. Maglev is short for magnetic levitation. A maglev train is an amazing vehicle. It doesn't touch the ground at all! It is suspended, or levitated, in the air above the track by magnetic force. Magnets in the track and magnets in the train repel each other, keeping the train levitated in the air just a little bit above the track. People started experimenting with magnetic levitation in the 1960s. Now several countries are working on projects to develop maglev trains to use for public transportation. Germany is leading the way with its Transrapid system. Japan is also developing maglev technology, and so is the United States. California and Maryland are two states that are working on maglev projects. Maglev trains will be able to travel up to 300 miles per hour. They use complicated technology that involves such things as coils, amplifiers, and negative feedback as well as magnetism. 1The force that happens when two things rub together is called friction magnetism electricity gravity 2Friction is useful a problem a force all of the above 3. One way to reduce friction is to reduce the amount of contact with the ground false true 4. One way to reduce friction is to use rough surfaces. false true 5. One way to reduce friction is to use a lubricant such as oil. false true 6. Boats have no friction because they do not travel on the ground. false true A 20.0 kg trunk is pushed across the floor of a moving van by a horizontal force. If the coefficient of friction between the trunk and the floor is 0.255, what is the magnitude of the frictional force opposing the applied force? 500 N 50N 5.1 N - 5.1 N The largest flowers in the world are found in Malaysia. A single flower is almost a meter across and has a mass up to 11.0 kg. Suppose you cut off a single flower and drag it along the flat ground. If the coefficient of kinetic friction between the flower and he ground is 0.39, what is the magnitude of the frictional force that must be overcome? - 4.29 N 4.29 N 422 N 42 N The heaviest train ever pulled by a single engine was over 2 km long. Suppose a force of 1.13 x 108 N is needed to overcome static friction in the train's wheels. If the coefficient of static friction is 0.741, what is the train's mass? 8.37 x 107 kg 1.55 x 107 kg 1.52 x 108 N -1.52 x 108 kg