Is the amount of sliding friction proportional to the roughness of the contact surface?

Friction is related to roughness and pressure, but it is not that the greater the pressure, the greater the friction.

Take the experiment as an example: use the following equipment (crochet box, hook code, spring scale, towel, newspaper, glass plate) to perform the experiment. Experiments show that the magnitude of sliding friction is related to the size of the contact area, and the larger the contact area, the greater the sliding friction.

The magnitude of sliding friction is related to the magnitude of the motion speed, and the faster the movement, the greater the sliding friction.

Physics is in life, and physics serves life and society. Where friction is to be used in life, we have to try to increase it, but sometimes friction brings us harm, and we have to try to reduce it. So how to increase friction and how to reduce friction?

1. Increase beneficial friction: increase the pressure and increase the roughness of the contact surface. Reduction of harmful friction: Reduced pressure and roughness of the contact surface.

2. "Catching the ball" on the football field is to increase friction by increasing pressure.

3: The sole of the travel shoes is uneven, which is to increase the roughness of the contact surface to increase the friction. 4: When performing the erhu, vigorously play and add rosin powder, which increases the pressure and increases the roughness of the contact surface to increase the friction.

5. When the belt is driven, the belt should be tightened and the belt wax should be added, which is to increase the pressure and increase the roughness of the contact surface to increase the friction.

This completely leads people into a misunderstanding, the magnitude of sliding friction has nothing to do with the size of the contact area, nor does it have anything to do with the speed; It is only related to the roughness of the contact surface and the amount of pressure.

Experimental report on the relationship between the magnitude of friction and the smoothness of the contact surface.

1. Research question: Is there a relationship between the magnitude of friction and the smoothness of the contact surface?

2. My speculation: the magnitude of friction is related to the smoothness of the contact surface (the smoother the contact surface, the less friction the object will experience; The rougher the contact surface, the greater the friction experienced by the object).

3. Different conditions: smoothness of the contact surface: a group of smooth contact surfaces; A set of contact surfaces is rough.

Fourth, the conditions that remain the same: the weight of the box, the shape of the box, the spring scale, and the speed at which the box is pulled.

Sixth, the experimental process:

1) Attach one end of the rope to the hook of the spring scale and the other end to the box.

2) On a smooth tabletop, gently pull the box at the same speed as the middle mold, find just enough force to make the box move, record the reading on the spring scale, and repeat 3 times.

3) Spread a layer of sand on the tabletop slippery, gently pull on the sand, find just enough force to make the box move, and make a record. and repeat 3 times.

7. Record Sheet:

Contact surfaces. Smoothness.

Frequency. Frictional force.

size. The conditions that do not change.

The contact surface is smooth.

1 The weight of the 5n box, the shape of the box, the spring scale, and the speed at which the box is pulled.

1 7n1 5n contact surface rough.

2．3n2．4n

2 3n VIII. My conclusion: The smoother the contact surface, the less frictional the object is subjected to; The rougher the contact surface, the more friction the object will experience.

(4) The purpose of the experiment is to draw the correct conclusion, and the more the experiment is conducted, the more true the conclusion of the comparative experiment

5) Because the magnitude of sliding friction is related to the magnitude of pressure and the roughness of the contact surface, when studying the relationship between the magnitude of sliding friction and the area of the contact surface, the pressure and the roughness of the contact surface should be kept unchanged

3) When the roughness of the contact surface is constant, the sliding friction force f is proportional to the pressure f;

4) The more data, the closer the relationship between the two is to the actual relationship (5) Incorrect; There is no control over the equality of pressure between objects

The rougher the contact surface, the greater the friction.

The force that hinders the relative motion (or relative tendency of motion) of an object is called friction. The direction of frictional force is opposite to the direction of the relative motion (or relative tendency of motion) of the object.

When an object slides on the surface of another object, friction occurs between the contact surfaces that hinders their relative motion, which is called sliding friction. The magnitude of sliding friction is related to the magnitude of the roughness of the contact surface and the magnitude of the pressure. The greater the pressure, the rougher the contact surface of the object, and the greater the sliding friction generated.

f= fn The rougher the contact surface, the greater the friction factor.

In general, the rougher the rougher, the greater the friction.

Friction is the "relative motion" of two objects that are in contact with each other and are about to occur, if there is or is about to occur between them, a frictional force that prevents this relative motion force will be created on the contact surface.

There are two factors that affect pressure friction, one is the amount of pressure, and the other is the roughness of the contact surface.

In experiments to study the relationship between the contact area and roughness and the friction force. Because of the shallow "degree", experiments usually collect 3 sets of data.

To study whether the contact area is related to friction, all that is required is a spring dynamometer and a cuboid with two different surface sizes; To study the relationship between roughness and friction, you need at least three surfaces with different roughnesses, such as glass, wood, towels, etc.

The friction force on the stationary object is the static friction force, and its magnitude should be found according to the force balance, and has nothing to do with the roughness of the contact surface, but the actual static friction is between zero and the maximum static friction, and the roughness of the contact surface can directly affect the maximum static friction.

The magnitude of sliding friction is directly related to the roughness of the contact surface, the rougher the contact surface, the greater the friction factor, and the greater the sliding friction under the same positive pressure.

Chapter 7 Motion and ForceSection 6 "What is the magnitude of friction related to the student's experiment".

1.Place the wooden block on the horizontal long wooden board and pull the wooden block horizontally with a spring dynamometer to do a uniform linear movement with variable speed, and read the dynamometer indication f1

2.Lay cotton cloth on a long wooden board and repeat the first step of the experiment to read the dynamometer number f23Spread a towel on a long wooden board and repeat the first step of the experiment to read the dynamometer number F34Comparative F1F2F3 analysis was concluded.

Chapter 7 Motion and ForceSection 6 "What is the magnitude of friction related to the student's experiment".

Experiment Name: Factors Affecting the Magnitude of Sliding Friction.

Purpose: To verify the relationship between the magnitude of sliding friction and the magnitude of pressure, the size of the contact area, and the roughness of the contact surface (the purpose of the experiment on the book, if the DIS system is used, sometimes such purposes should be added, such as: practice using the DIS system for linear fitting, practice using a stopwatch, etc., but these are not the main experimental purposes).

Experimental equipment: spring dynamometer, long wooden board, cotton cloth, towel, cuboid block with hook, weight, scale, stopwatch.

Experimental principle:1Condition for equilibrium of two forces: two forces acting on the same object, if they are equal in magnitude and opposite in direction, and are in the same straight line, the two forces are balanced.

2.Under the action of equilibrium force, the object at rest remains at rest, and the object in motion maintains a state of linear motion at a uniform speed.

3.When two objects in contact with each other are in relative motion or have a tendency to move relatively, a force will be generated on the contact surface that hinders the relative motion, which is called friction.

4.When the spring dynamometer pulls the wooden block to do a uniform linear motion on the horizontal plane, the magnitude of the tensile force is equal to the magnitude of the friction force, and the value of the tensile force can be read from the spring dynamometer, so that the friction between the wooden block and the horizontal plane is measured.

Experimental procedure: pull the wooden block at a constant speed with a spring dynamometer to make it slide along the long wooden board, so as to measure the friction between the wooden block and the long wooden board; change the weights placed on the block, thereby changing the pressure between the block and the long plank; Spread the cotton cloth on a long wooden board to change the roughness of the contact surface; Change the contact area by changing the contact surface of the block with the long plank.

Experimental data:1Pull the wooden block at a constant speed with a spring dynamometer to measure the friction between the wooden block and the long wooden board at this time

2.Add 50g of weights to the wooden block to measure the friction between the wooden block and the long wooden board at this time

3.Add 200g of weights to the wooden block to measure the friction between the wooden block and the long wooden board at this time

4.Lay cotton cloth on the wooden board and measure the friction between the wooden block and the long wooden board at this time

5.Speed up the speed of pulling the wooden block at a uniform speed, and measure the friction between the wooden block and the long wooden board at this time

6.Flip the block over so that another surface with a smaller area is in contact with the long plank, and measure the friction between the block and the long plank

If you verify Ohm's law, you can draw an image based on the data and use a calculator to fit the slope. ）

Conclusions:1The amount of friction is related to the pressure acting on the surface of the object, and the greater the pressure on the surface, the greater the friction.

2.The amount of friction is related to the roughness of the contact surface, and the rougher the contact surface, the greater the friction.

3.The amount of friction is independent of the area of the contact surface between the objects.

4.The magnitude of friction is independent of the speed of relative motion.

f=un, where u is the coefficient of friction, so it is related to the roughness of the contact surface.

Objective: To understand the factors that can affect the friction when an object slides on another object.

Experimental equipment: a towel, a spring dynamometer, a wooden board, a wooden block, two 100-gram weights.

Experimental Procedure:1The spring dynamometer is hung on the wooden block, and the suede and linear surface of the board, table top and towel are made in a uniform linear motion respectively, and the data of the friction force on the wooden block is recorded.

2.Add a 100 gram weight to the wooden block, and make a uniform linear motion on the suede and line surface of the wooden board, table top and towel respectively, and record the data of the friction force on the wooden block.

3.Add two 100 gram weights to the wooden block, and make a uniform linear motion on the suede and line surface of the wooden board, table top and towel respectively, and record the data of the friction force on the wooden block.

Test data: Wooden towel (suede).

Towels (line surface).

The table top is not weighted.

f=nf=f=f=plus 100 grams of weights.

f=f=f=f=plus 200 grams of weights.

f=f=f=f=Experimental conclusion: Through the above experiments, I have concluded that on the same surface, the friction experienced by the object in equilibrium is proportional to the positive pressure of the object, and the greater the positive pressure, the greater the friction force.

Objects of the same mass are subjected to different frictional forces when they slide on surfaces with varying degrees of roughness. The rougher the sliding surface, the greater the friction experienced by the object.

The magnitude of sliding friction is related to the degree of (pressure) and the degree of roughness of the contact surface.

However, it is important to note that the magnitude of the sliding friction is independent of the area of the contact surface.

f= n, which is the kinetic friction factor (related to the roughness of the contact surface), and n is the pressure.

pressure on the plane ; Roughness.