Actis Scenarios

Science/Friction Unit

Please click here to download this section in MS Word (.DOC) format.

Learning objectives

To know and understand that friction is a force which acts when two surfaces move against each other.
To know how to, and be able to, use a Force Meter to measure the force of friction using Newtons as a unit of Force.
To plan, carry out and draw conclusions from a fair test to investigate the force of friction.

Background

Children should already understand that gravity is a force which pulls objects to the centre of the earth.

Learning objectives	Activity suggestions	Assessment opportunities
To use and understand a Force Meter; to understand and know that forces are measured in Newtons.	Using a collection of Newton Meters of various sizes, give out a selection onto different tables. Demonstrate to the children how to use the hook to measure the force of gravity on a pencil case. Ask the children to measure the force of gravity on a variety of objects. Challenge them to discover why some of the Newton Meters are different. Children should collect and compare results with each other and use shared discussion time to reveal that different Newton Meters measure different degrees. Some measure up to 5 Newtons and are good for measuring lighter objects on which gravity has a small pull. Some Force Meters measure up to 20 or even 50 Newtons and are good for measuring heavier objects, upon which gravity has a greater pull. Extension Activity Children should draw their Force Meter as though it was measuring the force of gravity acting upon a pencil case held in the air. Ask children to label the different parts of the Force Meter and also the different forces which are acting at the time. In addition, children can draw a similar diagram this time with the pencil case sitting on a table, so that the Force Meter reads zero. Children should label the gravity pulling on the table and also the resistance the table offers. As the pencil case is gradually lifted from the table, the force of gravity on the pencil case (measured by the Newton Meter) increases, and the level of resistance from the table decreases.	Observe children testing the Force Meters. Check for accurate readings. More advanced children should be using different Force Meters to measure the force of gravity on the same item to compare their results. By outcome - some children could draw their arm holding the Force Meter and be encouraged to label the force of resistance of the spring.
To determine the level of knowledge about forces in the group. To understand that friction is a force which can slow objects down.	Ask the children to tell you about all the forces they have heard of and let them offer their explanations. Encourage children to talk in terms of pushing and pulling. (Use feedback from the children to assess their knowledge and fill in any gaps or identify learning points for the future). Place a toy car on a table or other flat surface. Ask the children to explain what force is acting on the car now. They should point out gravity pulls the car down to the Earth but the surface of the table offers resistance. Use your finger to gently push the toy car. Another force is now acting on the car, the force of your push (some children may now point out the force of friction). Take the car to the beginning of the table and ask the children to time how long it takes the car to stop (or ask them to make an estimate of time or distance as to where the car will end up). When the car has come to a stop, ask the children to offer explanations as to why. Explain to the children that a force called 'friction' is at work between the surface of the table and the wheels of the toy car. What would happen if there was no friction to slow down the toy car? (It would fall off the table and crash). Move the discussion onto real cars. What slows down real cars? The surface of the brake pad rubs against the wheel disc. This slows down the spinning of the wheel, slowing the car down. Ask the children to think of different types of friction at work, slowing things down. Ask them to draw 1 or 2 examples and clearly label the forces and how they are acting. Examples might include brakes of a car or bicycle, the gravel trap alongside a race track, long grass slowing down a moving ball, etc.	Observation and listening to children's responses. Use the children's diagrams and written explanations as evidence of their understanding.
To understand that friction is a force which is present when two surfaces rub against each other. To understand and know that when two smooth surfaces rub together the force of friction is less than when two rough surfaces rub together. To use the terms slide and grip to define friction.	Create a display of friction working in different places. Print out this image of a scene and show it to the children. Ask them to point out the forces in the picture, in particular the points of friction. Remind the children that friction is present wherever two surfaces are moving against each other. Children can colour the picture, and if you wish, design a colour scheme to represent friction, gravity, etc. Using the children on the ice or the slide as an example, ask children to give examples of when a small amount of friction is more useful than a lot of friction to slow something down . i.e. ice skating, slides, drawers opening and shutting. Compare the two surfaces rubbing together when a skater's blade slides along the ice and when a rubber tyre hits a sandy patch. Discuss smooth and rough surfaces and how the degree of friction will change between these situations. Ask children to talk in terms of slide or grip and how different surfaces encourage either a slide (ice, glass, smooth surfaces) or a grip (rubber, carpet, rough surfaces). Reinforcement activity To assess or reinforce this point ask children to draw ridiculous situations when friction is being used in the wrong way, i.e. glass tyres, cycling in sand, etc and explain or correct the mistake. Homework Ask children to bring in a shoe that is either very good for sliding or very good for gripping (if possible, both types).	Some children will point out that friction is taking place on the slide and the ice, although it is much less than the bike slowed down by the sand. Observation of comments during discussion. Keep this as records of understanding and use in display if desired.
To use the Force Meter to measure the force of friction in Newtons. (All learning objectives associated with Investigation Skills and reinforcement of knowledge about forces, in particular the force of friction.) To make a fair test. To ask appropriate question to be investigated. To make observations and measurements. To use simple equipment appropriately. To use measurements to draw conclusions. To decide whether conclusions agree with prediction. To review their work and the work of others.	Group children so they have an opportunity to explore the surface of each other's shoes, looking at similarities and differences and how much grip each shoe would have. (If you wish use wax crayons and paper to make a rubbing of different shoe treads - this will make a great addition to your display). Distribute the Force Meters and after a demonstration ask the children to measure the grip of a variety of shoes using the same surface. Similarly ask the children to test the grip of the surfaces (so that they should use the same shoe - you may wish to place a weight inside the shoe to make the readings a little easier to get). Children should record their results appropriately and share with the class. Alternatively Ask children to create their own investigation into which shoe/s has/have the best grip. They should plan their investigation carefully, detailing what they are going to find out, their prediction, their resources, their method and what their results collection will be (usually a table). Also ensure that children have detailed how their test will be 'fair' and any repeated measurements they might take. When carrying out the test, look out for accurate measuring skills and whether their investigation is the same as their plan. Children are often tempted to test different shoes on different surfaces. Of course in order to do a fair test, the same shoe should be used on different surfaces or different shoes on the same surfaces. Other variations could include having a wet surface to see how that might change results. OR Create a ramp and glue or nail different materials on the ramp (carpet, foil, cotton wool, sandpaper) and test to see which has the most grip (this is a more simple investigation opportunity for younger children). After carrying out the investigation children should write their conclusion. Remember to include an explanation into why results were different. Relate this to how friction works. i.e. The trainer was the shoe with the best grip because it had a rough surface rubbing against the floor. When two surfaces move against each other friction is present. A rough surface has a larger surface area which means the force of friction would be stronger than on a smooth surface where there are less particles moving against each other. Children can produce graphs to show their results and should have some opportunity to share these results and compare with the rest of the class.	If your children are studying for the SATs, it is required that they are given an Investigation Level. Use this as an opportunity to record each stage of the investigation process, planning, carrying out the test and collecting results, and conclusions. The most vital stage will be planning, particularly over whether to test different surfaces or different shoes. More advanced children will do repeat measurements and may also include a 'control'. All students should write a prediction and in order to improve their level, refer back to that prediction in their conclusion. Conclusions should also give evidence of scientific knowledge about friction (or any other forces they might include). It may also draw attention to any unusual or unexpected results and offer explanations for them.