Physics 11 Unit3key Question#26

Key Question# 26 Lab Report:

Factors Affecting Friction Purpose: To investigate the effect of various factors on the force of friction. Hypothesis: • I predict the heavier the weight, the more the elastic band will stretch and the greater the force of friction. • I predict the harsher the surface area the greater the elastic band will stretch and the greater the force of friction • I predict the faster you move an object, the lesser the elastic band will stretch thus the lesser the force of friction. Material and equipments used: Tissue box (400 grams) Jar of bubble gums (400 grams) Book (200 grams) Elastic bands (40 cm) Procedure: • • •

Attach the elastic band to the tissue box with a tape, drag it with a constant velocity 0.5 m/s, and measure the length of the elastic band. Increase velocity from 0.5 m/s to 1.0 m/s and measure the length of the elastic band Attach the elastic band to the jar of bubble gums to the elastic band, drag with constant velocity 0.5 m/s, and measure the length of the elastic band Add a book on the top of the tissue box, drag with constant velocity 0.5 m/s, and measure the length of the elastic band

Analysis: Analysis for weight factor Type of material Weight Box of tissue 400 g Box of tissue and 600 g book

Velocity 0.5 m/s 0.5 m/s

Measurement of stretch 40 cm 60 cm

Analysis for surface area factor Type of material

Weight

Velocity

Box of tissue Jar of bubble gum

400 g 400 g

0.5 m/s 0.5 m/s

Analysis for speed factor Type of material Weight

Velocity

Box of tissues Box of tissues

0.5 m/s 0.1 m/s

400 g 400 g

Measurement of stretch 40 cm 50 cm Measurement of stretch 40 cm 30 cm

Conclusion: I conclude the heavier the material the more force required thus the greater the force of friction. The smoother the surface the less force of friction is required, and also the faster the object is moving, the friction will be less than of those objects that are moving slower Answers to Key Questions: a) Measuring was the most difficult part in this investigation. Having good measuring tools could improve the results. Also using more than just two surfaces could also improve the accuracy of this investigation. Two people should be doing this experiment as one person will move the object and the other person will do the measurement; having to do this experiment on my own was not fun, and maybe my measurements were not that accurate. b) Given: Box of tissue weighs= 400 g Jar of bubble gum= 400 g Box to tissue stretch= 40 cm Jar of bubble gum stretch= 60 cm Required: Average kinetic coefficient of friction for the two surfaces (box of tissue surface and Jar of bubble gum surface) Calculation for average kinetic coefficient of friction for the box of tissue: Analysis: Ff = µ k FN µk = Ff / FN

FN = FG FG = mg Solution: FG = (0.4 kg) (9.8 m/s^2) = 3.92 N Therefore FN = 3.92 N Fnet = Fapp + FF Fnet = 0 because velocity is constant Fapp = FF Fapp = F= K ∆x (Hooke’s law) FF = F= K ∆x FG = 0.1 kg FG = 0.1 kg * 9.8 FG =0.98 N ∆x=0.1 m K= FG /∆x K= 0.98 N/ 0.1 m K= 9.8 N Distance stretched= 40 cm Convert units: 40 cm= 0.4 m F= (9.8 N) (0.4 m) F= 3.92 N Therefore FF = 3.92 N µk = Ff / FN µk = 3.92 N/3.92 N µk = 1.0 Calculation for average kinetic coefficient of friction for the jar of bubble gum: FG = (0.4 kg) (9.8 m/s^2) = 3.92 N Therefore FN = 3.92 N Fnet = Fapp + FF Fnet = 0 because velocity is constant Fapp = FF Fapp = F= K ∆x (Hooke’s law) FF = F= K ∆x K= 9.8 N Distance stretched= 60 cm Convert units: 40 cm= 0.6 m F= (9.8 N) (0.6 m)

F= 5.88 N Therefore FF = 5.88 N µk = Ff / FN µk = 5.88 N/3.92 N µk = 1.5 Paraphrase: The coefficient kinetic frictions for the two surfaces are 1.0 for the box of tissue, and 1.5 for the jar of bubble gum. The value of µ depends on the nature of the two surfaces in contact (type of material), it depends on whether the object is just starting its motion or whether it is already in motion (change in velocity when a=0), and also it depends on the Fn value (weight) So to reduce this value, you have to increase velocity (a=0), use smoother surface, and reduce the weight of the object.