David has taught Honors Physics, AP Physics, IB Physics and general science courses. He has a Masters in Education, and a Bachelors in Physics.
After watching this video, you will be able to explain why friction exists when two surfaces move alongside each other. We'll also conduct investigations to compare the amount of friction created by different materials. A short quiz will follow.
When you rub your hand along a dining room table, the surface might seem super smooth. But it's really not. If you looked at it through a microscope, you would see a landscape of peaks and valleys. And when you put two surfaces together, the peaks and valleys on the two objects will often fall into each other, creating grip... or friction. Friction is the resistance that one surface encounters when moving alongside another due to imperfections in those surfaces. Friction is a force: a push or a pull.
Friction reduces the motion of objects. Cars have to deal with rolling friction. Skiers have to deal with sliding friction (both static and kinetic). And airplanes are slowed down by air resistance, which could be described as another kind of friction. Today, we're going to investigate just how different the imperfections in those surfaces can be, and how the imperfections affect the motion of objects.
Physics Lab Steps
For this physics lab, you will need:
Materials to create a sturdy ramp (for example, a plank of wood and some books)
A shoe with no tread (or possibly just a wooden block)
Several materials that can be attached to the bottom of the shoe; for example, silk, felt, and sandpaper
And, a ruler or measuring tape
Step 1: Once you have your materials, set up a sturdy ramp on top of an otherwise level surface. The ramp will need to be fairly steep, so that all of the objects we use will still slide down it. So a bit of trial and error may be needed.
Step 2: Attach one of the materials to the shoe. You can wrap the piece all the way around it, and then attach it to itself in a loop using the stapler. The material should completely cover the bottom of the shoe and be held tightly.
Step 3: Mark a starting position at the top of the ramp and a stopping position at the bottom, using the duct tape. Measure the distance between the two positions using a ruler or measuring tape.
Step 4: Position the shoe so that the front of the shoe is behind the duct tape marking the starting position. Release the shoe and start the stopwatch at the same time.
Step 5: Stop the stopwatch when the FRONT of the shoe reaches the second mark, and note down the time on the stopwatch.
Step 6: Repeat five times.
Step 7: Attach a different material to the shoe and continue the process, completing five trials for each material. You can use a table to collect your data.
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So if you haven't already, now is the time to pause the video and get started.
Analyzing Your Data
Once you have your data, you can average each set of five trials, to find the average time it took for each material to move down the ramp. You can then calculate the average speed at which the shoe moved down the ramp for each material: average speed is equal to total distance divided by total time (s = d / t).
Finally, plot a graph of average speed for each material to present your data. Since material isn't a continuous value, this could just be a bar chart (though we more often use scatter plots in physics).
As you can see from your data, some surfaces resist motion far more than others. You should find that the rougher surfaces result in longer travel time, and therefore, more friction.
Friction is the resistance that one surface encounters when moving alongside another due to imperfections in the surfaces. This friction reduces the motion of objects. Cars have to deal with rolling friction. Skiers have to deal with sliding friction. And airplanes are slowed down by air resistance, which could be described as another kind of friction.
In this physics lab, we investigated how much the roughness of surfaces can vary, and saw that it has a huge impact on the motion of objects. Rough surfaces resist motion more than smooth surfaces. Therefore, rougher surfaces create longer travel times and have more friction.
Once you are finished, you should be able to:
Explain what causes friction
Describe how to demonstrate friction
Analyze your findings as part of the friction physics lab
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