Coefficient of Friction?
Break down the components of gravity parallel to and perpendicular to the incline, set at θ relative to the horizontal. Parallel to = mg sin θ Perpendicular to = mg cos θ The normal force is typically equal to the perpendicular gravity component, and the friction is equal to the normal force times the coefficient, μ. In this case, gravity and friction will go one way (negative) while the string tension pulls the opposite way (positive). Just as the block begins to move, we expect: 30 N - mg sin θ - μmg cos θ = 0 You have m (5.00 kg), you have g (9.8 m/s^2, you have θ (40°), so solve for μ.
Good reference :(a) http://physics.bu.edu/~duffy/semester1/c6_measuremus.html(b) How to measure friction?
Performing the experiment on a horizontal requires an external force and perhaps a spring scale as suggested in the other Quora answer. I suggest an easier alternative method simply using the weight of the object as an external force. This will yield the coefficient of friction between the sample of material and the surface in contact. Place a piece of material (any size) on a plank. Now slowly increase the angle of the plank until the material just begins to slip. The angle [math]\phi[/math] of the plank measured from the horizontal will give you the coefficient of friction [math]\mu[/math] using:[math]\mu=tan\phi[/math]
What is the coefficient of kinetic friction between two pieces of cardboard?
This is going to vary a lot depending on the type of cardboard. It's not easy to find values for this, but the link below (see Table 8 of the article) gives values between 0.464 and 0.673 depending on the size of the piece of cardboard. I wouldn't worry if your value is outside this range, though, because there will be a lot of variation between samples. Hope this helps.
What is the coefficient of kinetic friction between the block and the surface?
There are two types of frictional forces: static and kinetic. Static friction is friction that exists when an object is not moving; for example, if you placed block on a board and slowly raised the board, static friction would be what kept the block in place. However, eventually the force of gravity on the block would exceed static friction and the block would slide down the board. In your problem you are dealing with kinetic friction. The friction the results from motion. Kinetic friction always acts in the opposite direction of motion. The force of friction is equal to the normal force between the object and the ground multiplied by the coefficient of friction: Fr = μ*N where Fr is the resistive force of friction, μ is the coefficient of friction for the two surfaces (Greek letter "mu"), and N is the normal or perpendicular force pushing the two objects together. In the case out your question it is the weight of the block (mg) In your friction question you know Fr, the force of friction, is slowing the block down (negative acceleration). You can determine the Fr using Newton's second law. F=ma. The force of friction will be acting against the force of motion. Fr=ma. Fr=ma Fr=(1.38kg)(1.21m/s/s) Fr= 1.6698N We also know that Fr = μ*N. Fr=μ*(mg) Fr/(mg)=μ μ=(1.6698N)/[(1.38kg)(9.8m/s/s)] μ=0.123469388
One thing I have learned recently is that it matters how deep the gravel is. I have been putting gravel on my sloped driveway recently. Where the gravel is thin (1 or 2 layers deep), the traction is significantly better than where the gravel is thick (5 to 6 layers deep). I'm using 3/4" crushed gravel so the thin gravel is 1/2" - 1" and the thick gravel is 2-3".It also matters whether the gravel is crushed or round, and how much it has been pushed into the road bed. The round gravel that is freshly applied (not pushed into the road bed) is almost like marbles under the tires.I think that is why a thick layer isn't as effective. It doesn't embed into the road bed and the top gravel just keeps moving around on the gravel below it. If the gravel had more fine sand, it would pack together better, but then I have more risk of it washing down the slope. That already happened to me once.Obviously, this isn't a single number answer. At best, I think embedded gravel could be almost as good as asphalt. According to this source, that could be as good as 0.9. Friction and Friction CoefficientsWith fresh round gravel that rolls beneath the tires, it would be much lower. Maybe as low as 0.1 or 0.2
Smooth Ice on smooth, wet Ice has one of the lowest coefficients of friction for everyday materials. An air hockey table isn’t bad either.
How do you measure the coefficient of kinetic friction between sandpaper and wood?
*Use electronic scale to find the magnitudes masses *Glue or fix a piece of sand paper to the bottom of the mass *Keep the mass on the wood block, wood block should be horizontal *Attach the Newton spring scale to the mass. * Move the mass by pulling by the Newton spring scale, the scale should be horizontal. * Note down the reading of the Newton Spring Scale with the magnitude of the mass. * Do this about 5 times and take data. F = μR In this case F is the kinetic friction force μ is the coefficient of the kinetic friction , and R is the Reaction force in this case it equals to the weight of the mass μ = F/R so you can get 5 values for μ by using the data of the 5 instances we did the practical. By taking the median you can find a more accurate value for the coefficient of kinetic friction.
experimentally you take 2 surface (lets say a plastic block and a plastic surface). one element you keep on top of the other. Then slowly you tilt one surface(here you can tilt the plastic surface). At an certain angle the block will start moving down from the surface without any external force. From there you can back calculate the friction coefficient