Presentation on theme: "Lesson 4: What is friction?. Period 1 the amount resistance between two objects it happens when two objects rub together can create heat when you rub."— Presentation transcript:
Lesson 4: What is friction?
Period 1 the amount resistance between two objects it happens when two objects rub together can create heat when you rub your hands together, you create friction rubbing two balloons together creates friction a soccer ball rolling on grass will eventually stop due to friction
Period 2 Friction is the tension between two objects Rubbing your hands together is an example of friction and it creates heat Friction is an energy created by two things rubbing together Rubbing two sticks together will create a fire Breaking on a bike creates friction between tires and the surface Rubbing a balloon on your head creates static friction
Period 5 Depending on the surface, the force will differ. The surface of the block will cause the paper towel to rip. The rougher the surface, the block will move slower. The friction will be more or less depending on the surface. The friction will produce different amounts of temperature on each surface.
Period 6 Friction is a force that warms things up and slows things down Rubbing your hands together will cause heat Friction is the force of two objects pushing up against one another Two different types of friction are static and sliding When you push an object, it will eventually stop because of friction Ice skates against ice
Period 8 Rubbing your hands together creates friction Rubbing your socks on the carpet Driving a car and pressing the break causes friction between the tires and the road Friction slows things down and creates heat Two types of friction: sliding friction and static friction Tires wear out from friction. Tires on ice are slippery because ice does not have a lot of friction.
Inquiry 4.1: Pulling A Block Across Different Surfaces APK (Accessing Prior Knowledge): What kind of instrument do you think will be used to measure the force of friction? What is friction? Give an example. Think-Pair-Share: What do you know about friction?
We used a spring scale to pull a wooden block across 5 different surfaces: table top, wax paper, paper towel, fine sand paper, and coarse sand paper Tabletop Wax Paper Paper Towel Fine SP Coarse SP
9. In your science notebook record your answers to the following questions: A.Which surface required the greatest force to pull the wooden block across it? B.Which surface required the least force? C.Did the weight of your wooden block change as the surfaces changed? D.Review the variables for the lesson. Which variables did not change as you tested each surface? Be prepared to discuss your answers with the class.
A.Coarse Sandpaper – Why? B.Tabletop or Wax Paper – Why? C.The weight remained the same. D.Weight and surface area did not change. What was the dependent variable and what was the independent variable? Independent variable – surfaces; Dependent variable – force of friction Fine SandpaperCoarse Sandpaper
Inquiry 4.2: Changing The Weight APK (Accessing Prior Knowledge): Why is a bar graph a better way to present your data than a line graph? Explain “balanced forces” by giving an example from yesterday’s lab. Focus Question Inquiry 4.2: What will happen to the force needed to pull the block if you change the weight of the block?
The force of friction increased as the number of blocks (weight) increased.
Inquiry 4.3: Changing the Surface Area APK (Accessing Prior Knowledge): What variables did you change about the block each time you slid it across the surface? Without adding anything to the block, what can you do to change it? Focus Question: How does the force of sliding friction change when the surface area of the wooden block is changed?
In Inquiry 4.1 you changed the surface the block was on. In Inquiry 4.2 you changed the amount of blocks on a surface (the weight). By keeping the surface constant and without adding anything to the block, what can you change? – You can change the side of the block (the surface area) that you slide on the surface.
By putting the rubber band on the lower half of the block, there is more stability when you pull. The block will slide more smoothly and the spring scale will be easier to read.
Inquiry 4.1: Sliding A Block Across Different Surfaces The force of friction does change depending on the surface. Inquiry 4.2: Changing The Weight The force of friction increases as the weight (number of blocks) increases. Inquiry 4.3: Changing The Surface Area The force of friction does NOT change when the surface area is changed.
Lesson 4 Vocabulary Friction – a force that opposes the motion of an object. Balanced Forces – two forces acting in opposite directions on an object, but are equal in size. Sliding Friction – opposes the motion of objects across a surface. Static Friction – friction between two objects that are not moving. Normal Force – the support force exerted on an object that is in contact with another object (think of static friction) Force – a push or pull. Surface Area – the measure of the total surface of an object. For a block, the surface area of any side of the block is the side’s length multiplied by its width.
Sliding Friction This is also an example of balanced forces because motion is pushing one way and friction is pushing the other way; opposite in direction, but equal in size.