Friction Stops Motion

Transcription

1 activity Friction Stops Motion BROWARD COUNTY ELEMENTARY SCIENCE BENCHMARK PLAN Grade Quarter Activity SC.C... The student understands that the motion of an object can be described and measured. SC.H... The student knows that it is important to keep accurate records and descriptions to provide information and clues on causes of discrepancies in repeated experiments. SC.H... The student knows that a successful method to explore the natural world is to observe and record, and then analyze and communicate the results. SC.H... The student knows that to work collaboratively, all team members should be free to reach, explain, and justify their own individual conclusions. SC.H... The student knows that to compare and contrast observations and results is an essential skill in science. SC.H... The student knows that data are collected and interpreted in order to explain an event or concept. ACTIVITY ASSESSMENT OPPORTUNITIES The following suggestions are intended to help identify major concepts covered in the activity that may need extra reinforcement. The goal is to provide opportunities to assess student progress without creating the need for a separate, formal assessment session (or activity) for each of the 0 hands-on activities at this grade level.. Ask students to describe situations when friction is helpful and to explain why. (Answers will vary. Examples: Friction stops things from sliding, so car tires have friction with the road. We need friction when we walk.). Use the Activity Sheet(s) to assess student understanding of the major concepts in the activity. In addition to the above assessment suggestions, the questions in bold and tasks that students perform throughout the activity provide opportunities to identify areas that may require additional review before proceeding further with the activity. broward county hands-on science Quarter 9

2 0 activity Friction Stops Motion

3 activity Friction Stops Motion OBJECTIVES Students discover that friction is a force that resists motion. The students observe the effects of friction on a moving object discover how lubrication reduces friction between an object and the surface over which it moves suggest additional ways to reduce friction between objects SCHEDULE About 0 minutes VOCABULARY friction lubricant MATERIALS For each student Activity Sheet, Parts A and B pr safety goggles* For each team of two container, plastic push-pull meter ruler, dual-scale* set washers, stacked and taped (from Activity ) For the class btl detergent, liquid measuring spoon, Tbsp. mixing bowl* rolls paper towels* water (preferably access to a sink)* Delta Science Reader Force and Motion *provided by the teacher PREPARATION Make a copy of Activity Sheet, Parts A and B, for each student. Before class, dilute some liquid detergent in a bowl by mixing one part soap to two parts water. Pour about Tbsp. of the mixture into each plastic container, one container per team of two. Each team of two will need a push-pull meter, a stack of washers (taped, from Activity ), a plastic container with diluted detergent, a ruler, and some wet and dry paper towels for wiping off their hands and desktops. BACKGROUND INFORMATION Students know that in order to get an object to move, force must be applied to the object. But a moving object will not remain in motion forever. There are other forces acting on it that cause it eventually to slow down and stop. One such force is gravity. Another force is friction. Friction is a force that resists motion. Friction occurs whenever two objects rub against each other. The surfaces of all objects, no matter how smooth they may appear, contain tiny bumps and pits that cause the objects to broward county hands-on science Quarter

4 catch as they slide past one another. Such resistance slows the objects down, generates heat and noise, and can cause the surfaces of the objects to wear. Friction makes work harder because it increases the amount of force necessary to move an object and keep it in motion. The rougher the surface of the object, the greater the friction produced. The greater the friction, the more force needed to move the object. If the friction is stronger than the force that is applied to the object, the object will not budge. One way to reduce friction between two objects is to apply a layer of lubrication to the surfaces that touch. Lubricants are substances that reduce friction between surfaces by smoothing over the bumps and pits in the surface, allowing the objects to slide across each other with less resistance. In this activity, students will observe the effects of friction and lubrication on moving objects. Activity Sheet, Part A Friction Stops Motion. What did you feel when you rubbed your hands together? palms felt warm a. What did you hear? a swishing sound friction b. What caused this?. You applied motion lotion to your hands and rubbed them together. What did you feel?. Motion lotion is a kind of lubricant. What are lubricants used for?. Use your push-pull meter to slide your washers as shown. How far will your stack of washers move? Record your results. Did you use lubrication? Write yes or no. Amount of Force units units units units Distance Moved about / inches about inches about inches about inches (The chemical used in this activity is liquid detergent.) It was easier to rub hands together; palms did not heat up. to reduce friction O O Did You Use Lubrication? no no yes yes Distances will vary depending on the smoothness of the desktop surface. Activity Sheet, Part B Friction Stops Motion. How did using lubrication change your results? Adding motion lotion to the desktop reduced the friction between the stack of washers and the desktop, which caused the stack to travel farther with the same force.. What are two ways to get an object to move farther? a. apply more force to the object activity Friction Stops Motion b. reduce friction between the object and the surface over which it moves. What are some good lubricants? Why? Answers will vary: oil, soap, petroleum jelly, hand lotion because they are slippery. What are some other ways to reduce friction between moving objects? Possible answer: using wheels or cushions of air or magnets

5 Guiding the Activity Ask students to demonstrate what they do when their hands get cold. Ask students, How does rubbing your hands together help? Have all students rub their hands together vigorously for 0 to seconds. Ask them to notice what they feel and hear. Ask, What causes this? Write the word friction on the board and read it aloud. Tell students that friction occurs whenever two surfaces rub together. Explain that all objects, no matter how smooth they look, contain tiny bumps and pits in their surfaces that cause the objects to scrape and snag as they slide past each other. This resistance to movement is called friction. Distribute a copy of Activity Sheet, Parts A and B, to each student. Tell students to complete question, parts a and b. Additional Information Some students will blow on their hands, but others will rub them together. Students will probably say that it makes them feel warm. Students will probably say the rubbing. Divide the class into teams of two. Distribute a plastic dish with some diluted detergent in Safety Note: Caution students to handle it to each team. Tell students that you call the motion lotion carefully. Wipe up spills this substance motion lotion. immediately to prevent slips and falls. Ask, What do you think this substance does? Tell students to dip their fingers in the motion lotion and spread a generous amount on the palms of their hands. Then have them rub their hands together like they did before. Ask, What do you feel now? Write the word lubricant on the board. Explain that the motion lotion acts like a lubricant to reduce friction. Lubricants are slippery substances that coat and smooth the surfaces of objects so that the objects slide across each other more easily. Students may suggest that it helps things move better. Students should feel no heat this time. broward county hands-on science Quarter

6 Guiding the Activity Have students wipe their hands off with a wet paper towel (or rinse them in a sink) and dry them. Tell them to complete questions and on their activity sheets. Additional Information Then tell students that in this activity they are going to observe the effect of friction and lubrication on a moving object. Distribute a push-pull meter, a stack of washers, and a ruler to each team. Refill students dishes with motion lotion as necessary. Tell students to place their push-pull meters flat on their desk, with the handle closest to them. Have them place the stack of washers on the desk against the rubber band, pull the stack back against the band to units of force (like a slingshot), then release the stack so it slides along the desktop (see Figure -). The stack should slide forward, between the arms of the push-pull meter. Tell students to use their ruler to measure the distance that the washers traveled and to record the distance in the table of question on Activity Sheet, Part A. Ask, How far did your stack of washers slide? Answers will vary. For most teams, the stack of washers should slide across the desk about cm ( in.). Ask, What keeps the stack of washers from sliding any farther? activity Friction Stops Motion Students may say that the washers ran out of force. Guide students to understand that friction between the washers and the desktop slows the motion of the washers until they stop. O O Figure -. Using the push-pull meter to apply units of force to a stack of washers.

7 Guiding the Activity Ask, What can we do to make the stack travel farther? Have students repeat the experiment, this time using units of force. Tell them to measure the distance that the stack travels and to record the distance in the table of question on Activity Sheet, Part A. Then ask, How can we get the stack to travel farther without using any more force? Have students dip their fingers in some motion lotion and spread a thin track along the projected path of the stack of washers. Have them also dip the stack of washers into the liquid, then repeat the experiment using units of force, followed by units of force. Tell them to measure the distance that the stack of washers travels each time and to record the distances in the table of question on Activity Sheet, Part A. When students have finished, ask, How far did the stack of washers travel each time? Additional Information Students may suggest applying more force. Accept all answers. Students should find that the stack travels slightly farther with units of force. Students may suggest reducing friction by using lubrication on the bottom of the washers. Accept all reasonable answers. The stack should slide about twice as far as it did without lubrication. Ask, What caused the stack to slide farther? Ask students to answer questions and on Part B of their activity sheets. To conclude, ask, How does lubrication reduce the amount of force needed to move an object? Tell students to complete question on the activity sheet. Have volunteers read their answers aloud. The motion lotion acted as a lubricant to reduce friction between the desktop and the washers, enabling them to remain in motion longer and thereby travel farther. Lubrication works by reducing friction between two surfaces, allowing the surfaces to slide past each other more easily. broward county hands-on science Quarter

8 Guiding the Activity Tell students that lubricating fluids primarily oil are often used in machines to reduce the friction between moving parts. This makes the machines work more efficiently, more quietly, and at a cooler temperature. But it is not always possible or practical to use lubricants when you want to move things. Ask, What are some other ways to reduce the friction between moving objects? Tell students to answer question on their activity sheets. Tell students that in the next activity, they are going to learn about one of the most important inventions in history the wheel and how it can be used to overcome friction. As appropriate, read or review page of the Delta Science Reader Force and Motion. Additional Information Some students may suggest using wheels, cushions of air, or even magnets. Accept all answers, and review them as a class. R EINFORCEMENT Challenge students to find out how much force they need to use to get the washers to travel cm ( in.) with lubrication. (Answer: Students should discover that with lubrication the stack can be moved cm using about half the force that they needed without lubrication probably about units of force instead of.) SCIENCE JOURNALS Have students place their completed activity sheets in their science journals. activity Friction Stops Motion C LEANUP Give students wet paper towels and have them wipe their desks clean. Collect the push-pull meters, stacks of washers, and dishes of motion lotion (soap). Rinse and dry the stacks of washers and dishes and return them, along with the measuring spoon and bottle of liquid detergent, to the kit. SCIENCE AT HOME Point out that the soles of our shoes provide friction between our bodies and the surfaces we walk on. Show students how to do a sole imprint: cover the shoe sole with a piece of paper and rub over it lightly with a pencil to reproduce the pattern. Then invite them to compare the soles of family members shoes and bring in to class a rubbing of the sole they think will provide the most friction.

9 Connections Science Challenge Tell students that in many sports, athletes want to increase friction to prevent sliding or slipping. For example, baseball pitchers rub rosin on their hands to increase friction and improve their grip on the ball. Challenge students to brainstorm examples of other sports in which friction plays an important role. (Students might mention the sandpaper or rough rubber covering on a table tennis paddle, grooved soles on running shoes, rosin on gymnasts hands, and wax on crosscountry skis.) Science Extension Obtain an ice cube and a blunt knife. Tell students that you will try to cut through the cube, first by simply pressing down on the knife and then by sawing back and forth with it. After you have done this, ask: Which method was more successful? Why? (Sawing was more successful, because the friction of the knife against the cube creates heat that melts the ice.) You may want to tell students that ice skaters are actually skating on a thin film of water that the skate blades melt as they glide across the ice. Science and the Arts Ask a student, teacher, or parent who plays a bowed instrument such as a violin to demonstrate for the class how it is played. Explain that the sound production depends on friction between the bow and the strings and that the musician applies rosin to the bow to increase the friction. Science and Language Arts Ask students to think about what everyday life would be like if friction did not exist. Simple activities such as walking and writing would be impossible. Bicycles, cars, and other wheeled vehicles would not work because the wheels would spin without gripping the road surface. Encourage students to write poems, short stories, or humorous skits about life in a frictionless world. Science and Math Have teams of students carry out the following activity to measure the force required to overcome friction under various conditions. With strips of masking tape, mark starting and stopping lines at least one foot (0. cm) apart on a desk. Students can use the stack of washers from the activity or another object as a load. They then use the push-pull meter to pull the load from the starting line to the stopping line, recording the force of the pull that is required. Then repeat the experiment with the desk surface covered with different materials, such as aluminum foil, sandpaper, smooth fabric, terry toweling, waxed paper, and waxed paper coated with a thin film of motion lotion (diluted detergent). Record the results of each trial. When students have completed their experiment, help them make a bar graph showing the results. Have them label the horizontal axis Type of Surface and the vertical axis Average Units of Force. Science, Technology, and Society Tell students that scientists discoveries about friction have led to attempts to improve transportation by reducing friction between the vehicle and a surface. Two examples are air cushion vehicles, or ACVs (also known as hovercraft), and hydrofoils, which have special fins that lift the craft above the water when speed is attained. Encourage students to research these vehicles and report their findings to the class. broward county hands-on science Quarter

10 activity Friction Stops Motion