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Activity: Frictional force experiment

This content is provided by the 49ers Museum Education Program.


Forces affect the motion and speed of a football in the game, and different forces can help or hinder motion in the game at different times. Some forces are in direct contact with objects, while other forces are not. For example, the force of friction slows the football down when it rubs against another object. Friction is a force that resists motion between two bodies in contact. You can observe friction when you roll a football on the ground. The ball will eventually come to a complete stop after rolling, because the friction caused by the football dragging on the ground depletes the force that was initially enacted upon it.

Try it

To experience friction firsthand, put your hands together in front of you and rub your palms back and forth. Your hands probably got warmer, right? The heat was created by your hands resisting the motion between them.

Friction examples

Friction can be found all around you. We depend on friction to keep our feet from sliding out from under us and to keep us safe. Have you ever tried to slide on a gym floor wearing sneakers and then wearing leather-soled shoes? Sneakers have enough traction and enough friction to stop you from sliding. A leather-soled shoe has no traction, creating less frictional force that can stop your movement.
In football we often want to maintain contact with a surface to utilize “good” friction to our advantage, but at the same time, we might not want materials heating up or slipping, so players desire to minimize “poor” friction. The ability for a 49ers player to stop immediately on grass turf with cleats would be an example of good friction. The player would need some friction to stop, and to also have the ability of their cleats to grasp the fieldturf to slow down their momentum. An example of poor friction would be when a 49ers player is not wearing cleats and slips and falls when trying to come to an abrupt stop or change directions quickly. Another example of friction in action can be found in catching a football. The neoprene gloves that receivers wear provide friction on the football by the receiver gripping the ball with its sticky texture. This in turn makes the football slow to a stop and enables the football to be caught.

Friction experiment

Today you will be conducting an experiment with motion, frictional force, and learn how such frictional forces may affect the game of football.

Materials needed:

  • Three textbooks of different weight and dimensions
  • String (8 feet in length)
  • Three different testing surfaces like a table, carpet or tile floor
  • Scale
  • Tape Measure/yard stick
  • Stop-watches (if available)
  • 49ers Frictional Force Worksheet
Step 1
Collect three of your school textbooks that are different size and weight (you can use books of various sizes that you have at home as well).
Step 2
Record the weight of each of the books before experimenting.
Step 3
Find three different surfaces to slide (or push) the textbooks on (examples: table, carpet, tile floor, etc.).
Step 4
Being sure not to damage the textbook, slide the textbook along various surfaces, keeping a keen eye on the frictional force that each surface has on the movement of the textbooks.
Step 5
Record the time and distance that each book traveled on the three different surfaces on your provided 49ers Frictional Force worksheet.
Stop & think
What factors do you think affect the size of the frictional force? Explore combinations such as a sliding on different sides of the textbook, on different surfaces areas, or stacking books on top of each other, or combinations thereof. Come up with some predictions on how fast and far you think the textbooks will travel.
Step 6
Tie strands of string around each textbook, and this time, pull each book and record the time it takes to pull the same distance you pushed the book on the three surfaces. Write down your observations and record the times of this experiment.
Step 7
Answer the following question: What effect would friction have on a rolling football?
Hint: Footballs are different from the books you pushed and pulled in that they have a shape that when rolled, reduces friction. You may think that footballs are immune from friction, but the surface on which they roll have a lot to do with how much friction is applied to the football. And of course, gravity has the ability to slow the football down as well.

Conclusion & reflection

By participating in this experiment, you can easily conclude that textbooks do not normally move by themselves, they have to be moved by a force. As a conclusion to this activity, reflect upon the following questions concerning the magnitude of frictional force applied on the textbooks during testing:
  1. When you pulled the textbook towards you, you could feel a force opposing you. What force do you think is pushing against the book as you pulled it?
  2. What happens if you double the weight by stacking one book on top of the other? How does the surface type affect the frictional force? Typically the smoother the surface is the less friction. However, sometimes tile floor, which is very smooth, will produce a large frictional force, especially if it is very clean.

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