JUAN DELA CRUZ TEACHER F R I C T I O N ACTIVITY A “Push Mo Yan” Comparing Movements of Objects on Different Surfaces At the end of the activity, I can: A. Describe frictional force Infer how friction affect movements of objects. Explain the effects of friction. Materials: Block of wood Spring scale Sand paper Baby powder hook rods tape What you need to do: 1. Attach a piece of sand paper on one side of the block of wood. 2. Hook a spring scale to the block of wood. Place the wood on the table. (The sand paper should met the surface of the table.) 3. Using a steady force, use the spring scale to pull the wood across the table at a steady speed. Record the force applied to pull the block of wood across the table. 4. Remove the sand paper from the block of wood. Sprinkle a small amount of powder on the table. Repeat step 3. 5. Place several rods on the table. Place the block of wood on top of the rods. Then repeat step 3. Force Exerted (N) Kind of surface Smooth Surface Rough Surface Surface with rollers Trial 1 Trial 2 Trial 3 Average What have you found out? 1. What affects the motion of the block of wood?______________ 2. What kind of friction is shown when you let the block of wood with sandpaper slide on the surface of the table?____________________________________. 3. What kind of friction is shown when you let the block of wood roll on rods?______________________________________. 4. Under what condition was the frictional force smallest? 5. How do rollers help in decreasing the amount of force needed to pull the block of wood? What is friction? How does a friction affect the motion of an object? Friction opposes motion. It causes an object that moves along a surface to slow down and eventually stop. Does the amount of friction varies in every moving objects? A moving object is affected by friction. However, the amount of friction may vary depending on the type of surface the objects gets in contact with. Kinds of Friction Rolling Friction Sliding Friction When an object rolls over a surface, rolling friction is produced. Ex. In cycling, the weight of the rider and the bicycle presses the tires against the ground. This downward force creates increased friction between the tires, giving tire traction. If it were not for the friction, the tires could not push on the road surface to drive the rider forward. Sliding friction, also called dry friction, occurs when two objects rub against each other or slide against each other. Sliding friction is caused by chemical bonding between surfaces. Ex. When you move a block of wood on sandpaper, the movement of the wood is affected. Friction occurs on the surface of the wood and the sandpaper or even on the surface of the table or floor. The block of wood moves slowly, with more force needed to move it. Kinds of Friction Fluid Friction Static Friction Fluid Friction is friction between moving objects and a liquid or between an object moving in the air. Objects moving through fluid, either liquid or gas, experience drag. This drag slows down the motion of the object. Ex. Fluid friction occurs in a swimmer swimming in water, a boat travelling in water, or an airplane in the air. In a moving boat, drag acts between the surface of the boat and the water and between the sails and the wind. Static Friction occurs in stationary objects or at rest. It is a kind of friction that prevents an object from moving against surface. Ex. Static friction is shown in a notebook or any object placed on a table or any surface, which remains still. Friction keeps a notebook from sliding off a table, even when the table is slightly tilted. You can pick up an object without the object slipping through your fingers because of friction. Desirable Effects of Friction Friction allows us to grip things. You would be able to pick up anything with friction. You can hold and squeeze a ball because of friction. Friction helps people convert one form of motion into another. Friction allows people to walk . You move forward because there is friction between the surface of your shoes and the ground. Without friction, you will slip or fall and not be able to stand up. A cyclist uses friction to move forward. The friction between her/his legs shoes and the pedals and between the chain and gears is needed to move the bike. Friction converts some energy into heat. Friction is needed to produce fire. When you light a matchstick, friction is needed to change chemical energy in the matchbox and matchstick into light energy. Without matches, you can also produce fire by rubbing rubbing two stones ot sticks together. Undesirable Effects of Friction Friction makes objects difficult to move continuously. There is friction between the bottom or feet of furniture and the floor. When moving furniture, friction is undesirable. Friction converts some energy into heat, noise and wear and tear on materials. When a cyclist pedals on a bicycle, the energy exerted by the cyclist in converted into noise and heat. Too much heat can cause the wear and tear of the bicycle parts and reduce the efficiency of the bicycle. Excess frictional heat could damage the machine and the breaking system. This will result in periodic maintenance and replacement of some parts of the engines. Multiple Choice: Read each item carefully. Circle the letter of the best answer. 1. Which has the greatest friction? a. Polished floor b. Sandy floor c. Wet floor d. Tiled floor 2. The boat sailing on the sea slows down. What kind of friction is acting on it? a. Static friction b. Rolling friction c. Fluid friction d. Sliding friction 3. Which of the following statements best describes friction? a. It is a force that occurs between solids. b. It is a force that occurs only on rough surfaces c. It is a force that occurs between solids and liquids. d. It is a force that occurs when surfaces touch each other. 4. How can you best reduce friction between the bottom or feet of furniture and the floor? a. By smoothing the floor b. By keeping furniture on their place c. By applying lubricants like wax on the floor d. By putting wheels or rollers on the bottom or feet of furniture. 5. Which shows that friction is undesirable? a. Pushing furniture b. Lighting a matchstick c. Walking on wet floors d. Using the breaks when approaching a stoplight 6-10. Give example of situations where friction is applied.
