Content

• Steps
• Method 1 of 2: Rubbing Bodies Surfaces
• Method 2 of 2: Frontal Resistance
• Tips

Have you ever wondered why your hands get warm when you rub them against each other, or why you can make fire by rubbing two pieces of wood? The answer is friction! When two bodies move relative to each other, there is a frictional force that prevents such movement.Friction can cause energy to be released in the form of heat, warming hands, striking fire, and so on. The more friction, the more energy is released, so by increasing the friction between moving parts in a mechanical system, you will get a lot of heat!

Steps

Method 1 of 2: Rubbing Bodies Surfaces

1. 1 When two bodies move relative to each other, the following three processes can occur: irregularities on the surface of bodies interfere with the movement of bodies relative to each other; one or both surfaces of the bodies may deform as a result of such movement; atoms of each surface can interact with each other. All of these processes are involved in the occurrence of friction. Therefore, to increase friction, select bodies with an abrasive surface (such as sandpaper), a deformable surface (such as rubber), or a surface that has adhesive properties (such as sticky).
   • For more information on choosing materials to increase friction, see tutorials or online resources. For common materials, you can find their coefficients of friction (a quantitative characteristic of the force required to slide or move one material over the surface of another). The friction coefficients of some materials are listed below (the higher the coefficient, the greater the friction):
   • Aluminum to aluminum: 0.34
   • Wood to wood: 0.129
   • Dry concrete over rubber: 0.6-0.85
   • Wet concrete on rubber: 0.45-0.75
   • Ice on ice: 0.01
2. 2 Press the bodies closer to each other to increase friction, since the friction force is proportional to the force acting on the rubbing body (the force directed perpendicular to the direction of movement of the bodies relative to each other).
   • Think of disc brakes in a car. The more you press on the brake pedal, the more the brake pads are pressed against the wheel rim, the more friction becomes, and the faster the car stops. But the stronger the friction, the more heat is released, so when braking hard, the brake pads get very hot.
3. 3 If one body is in motion, stop it. So far, we have considered the sliding friction that occurs when bodies move relative to each other. Sliding friction is much less than static friction, that is, the force that must be overcome in order to set two contacting bodies in motion. Therefore, it is more difficult to move a heavy object than to control it when it is already moving.
   • Do a simple experiment to understand the difference between sliding friction and static friction. Place your chair on a smooth floor (not rug). Make sure there are no rubber or other pads on the chair legs to prevent sliding. Push the chair to move it. You will notice that once the chair is in motion, it becomes easier for you to push it because the sliding friction between the chair and the floor is less than the resting friction.
4. 4 Get rid of the grease between the two surfaces to increase friction. Lubricants (oils, petroleum jelly, etc.) significantly reduce the friction force between rubbing bodies, because the coefficient of friction between solids is much higher than the coefficient of friction between a solid and a liquid.
   • Do a simple experiment. Rub dry hands together and you will notice that their temperature has increased (they are warmer). Now wet your hands and rub them again. Now not only is it easier for you to rub your hands together, but they also heat up less (or slower).
5. 5 Get rid of bearings, wheels and other rolling bodies to get rid of rolling friction and get sliding friction that is much greater than the first (therefore rolling one body relative to another is easier than pushing / pulling it).
   • For example, imagine that you put bodies of the same mass in a sled and on a wheeled cart. A cart with wheels is much easier to move (rolling friction) than a sled (sliding friction).
6. 6 Increase the viscosity of the fluid to increase the frictional force. Friction takes place not only when moving solids, but also in liquids and gases (water and air, respectively). Friction between a liquid and a solid depends on several factors, for example, the viscosity of the liquid - the higher the viscosity of the liquid, the greater the frictional force.
   • For example, imagine that you are drinking water and honey through a straw. Water with a low viscosity will easily pass through a straw, but honey, which has a high viscosity, will hardly pass through a straw (since the honey rubs more against the walls of the straw).

Method 2 of 2: Frontal Resistance

1. 1 Increase your body surface area. As noted above, when solids move in liquids and gases, a friction force also arises. The force that prevents the movement of bodies in liquids and gases is called frontal resistance (sometimes called air resistance or water resistance). Frontal resistance is greater with an increase in body surface area, which is directed perpendicular to the direction of movement of the body through a liquid or gas.
   • For example, take a 1 g pellet and a sheet of paper of the same weight and release them at the same time. The grain will immediately fall to the floor, and the sheet of paper will slowly sink down. Here the principle of drag is just visible - the surface area of ​​the paper is much larger than that of a pellet, so the air resistance is greater and the paper falls to the floor more slowly.
2. 2 Use a body shape with a high drag coefficient. By the area of ​​the body surface directed perpendicular to the movement, it is possible to judge about the frontal resistance only in general terms. Bodies of different shapes interact with liquids and gases in different ways (when bodies move through a gas or liquid). For example, a round flat plate has more drag than a round ball-shaped plate. The value characterizing the drag of bodies of various shapes is called the drag coefficient.
   • For example, consider an airplane wing. The shape of an airplane wing is called the airfoil. It is a sleek, narrow and rounded shape with a low drag coefficient (about 0.45). On the other hand, imagine that an airplane wing is shaped like a square, rectangular prism. For such wings, the drag would be enormous (this is true, since the drag coefficient of a square rectangular prism is 1.14).
3. 3 Use less streamlined bodies. As a rule, large cubic bodies have high drag. Such bodies have rectangular corners and do not taper towards the end. On the other hand, streamlined bodies have rounded edges and usually taper towards the end.
   • For example, compare a modern car and a car made several decades ago. Old cars were square, while modern cars have many smooth curves. Therefore, modern cars have less drag and require a lower engine power (which leads to fuel economy).
4. 4 Use bodies without through holes. Any through hole in the body reduces drag by allowing air or water to flow through the hole (holes reduce the body surface area perpendicular to movement). The larger the through holes, the lower the drag. This is why parachutes, which are designed to create a lot of drag (to slow down the speed of the fall), are made of durable, lightweight silk or nylon, not gauze.
   • For example, you can increase the speed of your ping-pong paddle by drilling multiple holes in the paddle (to reduce the surface area of ​​the paddle and reduce drag).
5. 5 Increase body speed to increase drag (this is true for bodies of any shape and material). The higher the speed of an object, the greater the volume of liquid or gas it must pass through and the greater the drag. Bodies moving at very high speeds experience tremendous drag, so they must be streamlined; otherwise, the force of resistance will destroy them.
   • For example, consider the Lockheed SR-71, an experimental reconnaissance aircraft built during the Cold War. This aircraft could fly at a high speed of M = 3.2 and, despite its streamlined shape, experienced enormous drag (so great that the metal from which the aircraft fuselage was made expanded when heated due to friction).

Tips

• Remember that friction releases a lot of energy in the form of heat. For example, do not touch the car's brake pads immediately after braking!
• Keep in mind that high resistance forces can lead to the destruction of a body moving in a fluid. For example, if during a boat trip you put a piece of plywood in the water (so that its surface is perpendicular to the movement of the boat), then most likely the plywood will break.