Read the following information on Friction. Once you have read the information, follow the link at the bottom to answer the friction questions.
Friction
Picture a warm summer day. You are enjoying the day by wearing shorts and tossing a ball with your friends. By accident, one of your friends tosses the ball just out of your reach. You have to make a split-second decision to dive for it or not. You look down and notice that if you dove for it, you would most likely slide across pavement rather than the surrounding grass. What would you decide?
Unless you enjoy scraped knees, you probably would not want to slide on the pavement. The painful difference between sliding on grass and sliding on pavement has to do with friction. Friction is a force that opposes motion between two surfaces that are touching.
The Source of Friction
Friction occurs because the surface of any object is rough. Even surfaces that look or feel very smooth are actually covered with microscopic hills and valleys. When two surfaces are in contact, the hills and valleys of one surface stick to the hills and valleys of the other surface. This contact causes friction even when the surfaces appear smooth.
The amount of friction between two surfaces depends on many factors, including the roughness of the surfaces and the force pushing the surfaces together.
Rougher Surfaces create more friction
Rougher surfaces have more microscopic hills and valleys. Thus, the rougher the surface, the greater the friction. Think back to the pavement vs. grass example. Pavement is much rougher than grass. Therefore, more friction is produced when you slide on the pavement than when you slide on grass. This increased friction is more effective at stopping your sliding, but it is also more painful! On the other hand, if the surfaces are smooth, there is less friction. I you were to slide on ice instead of on grass, your landing would be even more comfortable – but also much colder!
Greater Force Creates More Friction
The amount of friction also depends on the force pushing the surfaces together. If this force is increased, the hills and valleys of the surfaces can come into closer contact. This causes the friction between the surfaces to increase. Less massive objects exert less force on surfaces than more massive objects do. For example, there is more friction between a more massive book and the table than there is between a less massive book and a table. A harder push is needed to overcome friction to move the more massive book. However, changing the amounts of the surfaces that touch does not change the amount of friction.
Types of Friction
The friction you observe when sliding books across a tabletop is called sliding friction. Other types of friction include rolling friction, fluid friction, and static friction. As you will learn, the name of each type of friction is a big clue as to the conditions where it can be found.
Sliding Friction
If you push an eraser across your desk, the eraser will move for a short distance and then stop. This is an example of sliding friction. Sliding friction is very effective at opposing the movement of objects and is the force that causes the eraser to sop moving. You can feel the effect of sliding friction when you try to move a heavy dresser by pushing it along the floor. You must exert a lot of force to overcome the sliding friction.
You use sliding friction when you go sledding, when you apply the brakes on a bicycle or a car, or when you write with a piece of chalk.
Rolling Friction
If the same heavy dresser were on wheels, you would have an easier time moving it. The friction between the wheels and the floor is an example of rolling friction. The force of rolling friction is usually less than the force of sliding friction. Therefore, it is generally easier to move objects on wheels than it is to slide them along the floor.
Rolling friction is an important part of almost all means of transportation. Anything with wheels-bicycles, skateboards, cars, trains and planes – use rolling friction between the wheels and the ground to move forward.
Fluid Friction
Why is it harder to walk on a freshly mopped floor than on a dry floor? The reason is that on the wet floor the sliding friction between your feet and the floor is replaced by fluid friction between your feet and the water. In this case, fluid friction is less than sliding friction, so the floor is slippery. The term fluid includes liquids, such as water and milk, and gases, such as air and helium.
Fluid friction opposes the motion of objects traveling through a fluid. For example, fluid friction between air and a fast moving car is the largest force opposing the motion of the car. You can observe this friction by holding your hand out the window of a moving car.
Static Friction
When a force is applied to an object but does not cause the object to move, static friction occurs. The object does not move because the force of static friction balances the force applied. Static friction disappears as soon as an object starts moving, and then another type of friction immediately occurs like sliding friction.
Friction Can Be Harmful or Helpful
Think about how friction affects a car. Without friction, the tires could not push against the ground to move the car forward and the brakes could not stop the car. Without friction, a car is useless. However, friction can cause problems in a car too. Friction between moving engine parts increases their temperature and cause the parts to wear down. A liquid coolant is added to the engine to keep it from overheating, and engine pars need to be changed as they wear out.
Friction is both harmful and helpful to you and the world around you. Friction can cause holes in your socks and in the knees of your jeans. Friction by wind and water can cause erosion of the topsoil that nourishes plants. On the other hand, friction between your pencil and your paper is necessary for the pencil to leave a mark. Without friction, you would just slip and fall when you tried to walk. Because friction can be both harmful and helpful, it is sometimes necessary to reduce or increase friction.
Some Ways to Reduce Friction
One way to reduce friction is to use lubricants. Lubricants are substances that are applied to surfaces to reduce the friction between them. Some examples of common lubricants are motor oil, wax, and grease.
Friction can also be reduced by switching from sliding friction to rolling friction. Ball bearings are place between the wheels and axles of in-line skates and bicycles to make it easier for the wheels to turn by reducing friction.
Another way to reduce friction is to make surfaces that rub against each other smoother. For example, rough wood on a park bench is painful to slide across because there is a large amount of friction between your leg and the bench. Rubbing the bench with sandpaper makes it smoother and more comfortable to sit on because the friction between your leg and the bench is reduced.
Some ways to Increase Friction
One way to increase friction is to make surfaces rougher. For example, sand scattered on icy roads keeps cars from skidding. Baseball players sometimes wear textured batting gloves to increase the friction between their hands and the bat so that the bat does not fly out of their hands.
Another way to increase friction is to increase the force pushing the surfaces together. For example, you can ensure that your magazine will not blow away at the park by putting a heavy roc on it. The added mass of the rock increases the friction between the magazine and the ground. Or if you are sanding a piece of wood, you ca sand the wood faster by pressing harder on the sandpaper.
Click on the following link to answer the friction questions
Friction Questions
