Vector diagrams are diagrams that depict the direction and relative magnitude of a vector quantity by a vector arrow In a vector diagram, the magnitude of a vector quantity
GRADE 11 SUBJECT Physical Sciences WEEK 2 TOPIC Normal and Static friction: Time 60mins Lesson
LESSON SUMMARY FOR: DATE STARTED: DATE COMPLETED:
LESSON OBJECTIVES
At the end of the lesson learners should be able to:
• Investigate the relationship between the normal force and the maximum static friction
• Apply equation to solve problems
TEACHING and LEARNING ACTIVITIES 1. TEACHING METHOD/S USED IN THIS LESSON:
Question and Answer
2. LESSON DEVELOPMENT 2.1 Introduction
a) PRE-KNOWLEDGE learners need understanding of the following:
(i) Normal force on the horizontal and on the slope ii) Frictional forces
b) BASELINE ASSESSMENT (educator to design a worksheet/ transparency or write questions on the board [preferably a worksheet to save time] to gauge the learners memory of their relevant prior knowledge)
QUESTIONS for the BASELINE ASSESSMENT [5 min] i) Define static friction
ii) A 5 kg wooden block is resting on the surface of the horizontal table. Find the magnitude and direction Normal force on the block iii) Write an equation used to calculate coefficient of static friction
Solutions
i) Is the maximum force needed to change the object’s state of rest
ii) Normal force for an object lying on the horizontal surface is equal to weight of an object but opposite in direction. weight (w) = mg
= 5 x 9,8
= 49 N downwards
∴
Normal force (N) = 49 N upwards2.2 Main Body (Lesson presentation) [30 min] Theory revision
The force needed to start motion is numerically equal to the maximum static friction. [Fs(max )]) (include the laws governing friction such as static friction is greater than kinetic friction
etc.)
The normal force is equal to the weight of the object.
The coefficient of the static friction (s) can be solved using this equation:
s = 𝑀𝑎𝑥𝑖𝑚𝑢𝑚𝑁𝑜𝑟𝑚𝑎𝑙𝑠𝑡𝑎𝑡𝑖𝑐𝐹𝑜𝑟𝑐𝑒𝑓𝑟𝑖𝑐𝑡𝑖𝑜𝑛
Aim : To investigate the relationship between a Normal force and the maximum static friction Apparatus : wooden block, wooden board, spring balance, 100 g mass pieces
Method/ Procedure :
wooden surface Fig. 1: Experimental set-up for determining force and friction
• Place a block of wood on a wooden board and attach the spring balance on the side with a hook as in the diagram above
• The maximum static friction was determined by slowly pulling the spring scale until the stationary block of wood moved.
• Record the maximum static friction
• The group repeated the procedure three (3) times and recorded their readings (in Newtons) on a table. Results
This table shows the reading of the maximum static friction and kinetic friction (in Newtons) Trial no. Fsmax
1 2 3 4
• For the second experiment, the block of wood was weighed using the spring scale. (in grams)
• The group then added 100g on the block of wood and did the same procedure in the first experiment.
• The group do 4 trials for this experiment. After recording the readings, the group then solved for the coefficient of static friction s = 𝑀𝑎𝑥𝑖𝑚𝑢𝑚𝑠𝑡𝑎𝑡𝑖𝑐𝑓𝑟𝑖𝑐𝑡𝑖𝑜𝑛
𝑁𝑜𝑟𝑚𝑎𝑙𝐹𝑜𝑟𝑐𝑒
This table shows the reading of the maximum static friction and kinetic friction (in Newtons) Trial no. Fsmax
1 0.80N
2 1.00N
3 0.90N
Normal force Fsmax s
2.80N 1.40N 3.00N 1.20N 3.00N 1.40N 2.80N 1.20N
The table shows the reading of the Normal force, kinetic friction (in Newtons). The table also shows the coefficient of static friction which was solved using the formula. (Note that the coefficient doesn’t have units since dividing the friction from the normal force will cancel out the unit Newtons.) Weight of block: 1.8 Newtons
Activity 2
For the this experiment, a block of wood, a wooden board, tiles (on the table), a plastic cover, paper, and the sand-paper side of the block of wood were used. The same
procedure was also done but varied on the surface which the block of wood was placed. The following surfaces were: wood to wood, wood to tile, wood to sand paper, wood to plastic cover and wood to paper. The group recorded their readings on a table
The table shows the readings of the static friction and kinetic friction on wood, tile, sand paper, plastic cover and paper. The group saw that when the surface is smooth, the static and kinetic frictions are lower and higher when the surface is rough.
Surface in Contact Fsmax
Wood and wood 0.80N
Wood and tile 0.70N
Wood and sand paper 1.20N
Wood and paper 0.50N Analysis of results : interpret graph
Sources of errors : What can be done differently to improve the results
Conclusion : How are the results of the experiment related to the aim of experiment 2.2 Learners Activities [15 min]
[ Educators need to add more questions such as one word and multiple choice questions which could not be included because of space ] A 50 kg box is at rest on a horizontal surface. When an 80 N force is applied to the box, it slides on the surface with a constant velocity. 50 kg
F 2.2.1 .1 Define static friction
2.2.1.2 Draw a labelled free body diagram for the box when it is ... moving at constant velocity. 2..2.3 Calculate the coefficient of friction.
2.2.4 How will the force of friction change if:
2.2.4.1 an identical box is placed on top of the 50 kg box
2.2.4..2 the same force is applied on another 50 kg box with a larger surface area? Write only INCREASES, DECREASES or STAYS THE SAME.
2.2.1 static friction is the maximum force that is needed to change the object’s state of rest 2.2.2 2.3 Conclusion
Answers
2.2.3 Ff = μkN 80 N = μk500 N µk = 0,16 2.2.4.1 Increases 2.2.4.2 Stays the sameReflection/Notes:
Name of Teacher: HOD:
Sign: Sign:
Date: Date:
Activity to reinforce lesson (Educator may summarise the main aspects of the lesson) [5 min.]
HOMEWORK QUESTIONS/ ACTIVITY (educator must give learners a few questions to answer at home by either writing them on the chalkboard or giving an exercise from the prescribed textbook) [30 min]