Basics, Types, Use and Applications

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2 Basics, Types, Use and Applications 2015 by Brilliant Classes

3 2015 by Brilliant Classes Science : Physics Unit : Friction Friction : Basics, Types, Use and Applications The following topics are included in this Unit: Definition of FRICTION with example Basics of Friction Scientific meaning of Friction Principal of Friction Coefficient of Friction Causes of Friction Types of Friction with numerous examples: Dry friction 1. Static friction 2. Sliding friction Fluid friction Rolling friction Determination of Friction Methods to reduce Friction Usefulness of Friction Fun-facts about the Friction Effect of Friction on moving objects Student worksheets/friction Lab exp. for the assessment and review of their knowledge

4 Science : Physics Unit : Friction Basics of Friction Suppose you decide to ride a skateboard. You push off the ground and start moving. According to Newton s First Law of Motion, if no other forces are acting on your skateboard, you will continue to move.but. What happens? Your skateboard slows down because of friction. The amount of friction depends on two things: 1. Kind of surface. 2. Forces pressing the surfaces together by Brilliant Classes

5 2015 by Brilliant Classes Science : Physics Unit : Friction Scientific meaning of Friction : Friction is a force. A frictional force arises when two substances contact each other. Friction is the resistance of motion when one object rubs against another. Friction works against the motion and acts in the opposite direction. For example when you try to push a toy car along the floor.

6 2015 by Brilliant Classes Science : Physics Unit : Friction Principles of Friction : Friction acts parallel to the surface that are in contact. The direction that friction acts is OPPOSITE the direction of the motion (or intended motion). F normal F friction(k) F applied F weight Co-efficient of Friction : Frictional Force, both static and kinetic, is directly proportional to the force pressing the two surfaces together. The more weight, the more friction. F friction static F F normal friction (static) F F F friction normal normal (μ = Co-efficient of friction) kinetic F friction (kinetic) F normal

7 Science : Physics Unit : Friction Causes of Friction : Even though a surface may look smooth, if you magnify the surface it isn t smooth. Everything is made of molecules. The molecules come together to make bumps. Some surfaces have molecules that leave large bumps and some leave smaller bumps, but all surfaces have bumps. Microwelds occur when two bumpy surfaces are rubbed up against each other they stick together. The greater the force on the object, the greater the force of the microwelds and the greater force is needed to overcome the microwelds to move the object. When one object is sliding on another it starts to slow down due to the friction. This means it loses energy. The energy doesn't disappear it changes from moving energy (also called as kinetic energy) to heat energy. This is why we generally use to rub our hands together when its cold. By rubbing them we generate friction and, therefore, the heat by Brilliant Classes

8 2015 by Brilliant Classes Science : Physics Unit : Friction Types of Friction : 1. Dry Friction : Dry friction occurs when two solid objects touch each other. There are two types under dry friction. a) Static Friction : It prevents an object from moving when force is applied means static friction tries to keep an object at rest. Ex : Walking - For each step you take pushes against the Earth. Without the friction, you would slip and fall with each step. Pushing Force b) Kinetic or Sliding Friction : It slows down an object that slides. No No Motion Friction Motion Static Friction Pushing Force Sliding Friction Friction

9 2015 by Brilliant Classes Science : Physics Unit : Friction Ex : If you push a box across the room, there is sliding friction between the bottom of the box and the floor. Ex : Rubbing Hands etc. 2. Fluid Friction : Fluid friction involves a fluid or air. The air resistance on an airplane or water resistance on a boat is fluid friction. Air pushes against you It acts on the forward moving part of the object Ex : 1. Front of the car 2. When you ride bicycle, the air pushes your hair and the clothes back. Fluid Friction 3. Rolling Friction : Rolling friction occurs when a round surface rolls over a surface, like a ball or wheel.

10 2015 by Brilliant Classes Science : Physics Unit : Friction It allows the wheels to turn by pushing back so tire moves forward. Ex : Bicycle or car etc. Ex : When you ride your bike through water there may not be enough friction between the tire and the ground to move forward and so the bike skids.

11 2015 by Brilliant Classes Science : Physics Unit : Friction Determination of Friction : a) F f_max = F N b) F f_max is the maximum force of friction c) (Mu) is the coefficient of friction d) F N is the normal force e) Friction can range in value from -F f_max to +F f_max f) depends on the types of surfaces that are interacting. It would be low for rubber on ice, but high for rubber on asphalt. It also depends on whether the surfaces are moving relative to each other ( static or dynamic ). g) Measures of friction are based on the type of materials that are in contact. Concrete on concrete has a very high coefficient of friction. That coefficient is a measure of how easily one object moves in relationship to another. h) When you have a high coefficient of friction, you have a lot of friction between the materials. Concrete on concrete has a very high coefficient and Teflon on most things has a very low coefficient. i) Teflon is used on surfaces where we don't want things to stick; such as pots and pans.

12 2015 by Brilliant Classes Science : Physics Unit : Friction Methods to reduce the Friction : Sometimes we want to reduce friction. For example, moving parts inside a car engine are lubricated with oil, to reduce friction between them. The oil holds the surfaces apart, and can flow between them. The reduced friction means there is less wear on the metal and less heat produced. In some cases we want to prevent friction so it's easier to move. A good example of this is a ball or wheel. They roll to help reduce friction. Lubricant like grease or oil. Ex. : Machines and engines use grease and oil to reduce friction and wear so they can last longer. To change the types of materials in contact with one another. Ex, ice contacting with steel would produce less friction than rubber would on concrete. This is why ice skates slide so easily on the ice, but you don't slip when wearing rubber shoes on the sidewalk. These different materials are said to have different "coefficients of friction".

13 2015 by Brilliant Classes Science : Physics Unit : Friction Use of Friction : Friction is also a great boon to us. After all, we would all just be sliding around everywhere if there wasn't friction to keep us steady. Friction is also used in car brakes, when we walk or climb a hill, in sandpaper, making a fire and more. Ice causes very little friction, which is why it is easy to slip over on an icy day. But this is a good thing for ice skating and sledging. Fun facts about Friction : Although wheels are great for rolling and reducing friction, they couldn't work without friction. It would be really tough just to stand up without friction. Friction can generate static electricity. The harder two surfaces are pressed together, the more force it takes to overcome the friction and get them to slide. Effect of Friction on a moving object? All kinds of friction cause moving objects to slow down or stop. The frictional force is found by multiplying the objects weight by a coefficient of friction.

14 2015 by Brilliant Classes Science : Physics Unit : Friction The value of co-efficient of friction is usually less than one, but can be higher than one (for example with rubber tyres on dry tarmac). Therefore friction requires a greater force to be applied to move the object. Friction is a force that acts against a moving object to slow it down. A type of friction is air resistance. Friction opposes the direction in which the object is moving, causing the object to decrease in speed or stop all together.

15 Name: 2015 by Brilliant Classes Date: Worksheet 1 1. Circle the pictures that show gravity in red. 2. Circle the pictures that show friction in blue.

16 Name: 2015 by Brilliant Classes Date: Worksheet 2 Draw an Illustration and describe examples of friction that occur around you.

17 Name: 2015 by Brilliant Classes Date: Worksheet 3 Draw an Illustration and describe examples of friction that occur around you.

18 Name: 2015 by Brilliant Classes Date: Worksheet 4 Complete the chart below. Type of friction Definition & Example Dry friction Static friction Sliding friction Fluid friction Rolling friction

19 Name: 2015 by Brilliant Classes Date: Worksheet 5 Draw an arrow to show where friction is occurring in each picture.

20 Name: 2015 by Brilliant Classes Date: Worksheet 6 Write as many words or phrases about the Friction. Friction

21 Name: 2015 by Brilliant Classes Date: Worksheet 7 Prepare Friction K W L chart What do you know about the Friction? What do you want to know about the Friction? What did you learn about the Friction?

22 Name: 2015 by Brilliant Classes Date: Friction Lab Exp. 8 Which type of material will create the least amount of friction for a car when it is going down a ramp? Imp : Directions for this Lab is given on the last page. Type of material How far the car went (Cm) Carpet / Tile Sand paper Wax paper Bubble wrap Conclusion: had the least amount of the friction.

23 2015 by Brilliant Classes Name: Date: Friction Lab Exp. 8 Imp : Directions for the friction Lab : During this lab divide your students into groups (Three or four). Give required materials to each group: The students will be making the car go down the ramp to see how friction affects how far the car will go. Here are the steps: 1.Have the students place the binder on floor. If you have carpet or tile, tick proper surface type and record the readings. 2. Explain to the students they will be making the car go down the ramp (binder) and measuring how far the car goes. Tell students to measure from the edge of the binder to the end of the car to keep it consistent. DO NOT PUSH THE CAR! Let gravity do the work. 3. The students will release the car from the top of the binder and then measure how far it goes. They will then record the measurement. 4. The sandpaper is next. I use about one foot. The students feel the paper to see how rough it is. Then, have them open the binder and place a bit of the sandpaper in the binder. Most of the paper will be sticking out. This is to create a smooth transition from the binder to the sandpaper. Have the car go down the ramp and measure. 5. Repeat with the wax paper and the bubble wrap. 6. Now create a chart with all the groups results together and talk about making sure an experiment is reliable. 7. Make the conclusion for all the cases.

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