Physical inquiry experiment: factors affecting friction
Inquiry preparation
Skill preparation:
Spring dynamometer, long board, cotton cloth, towel, hook cuboid block, weight, balance, stopwatch.
Knowledge preparation:
1. Conditions for the balance of two forces: If two forces acting on the same object are equal in magnitude and opposite in direction and on the same straight line, the two forces are balanced.
2. Under the action of the balancing force, the stationary object remains in a static state, and the moving object maintains a uniform linear motion state.
3. When two objects are in contact with each other, when they are in relative motion or have a tendency to be in relative motion, there will be a force on the contact surface that hinders the relative motion. This force is called friction.
4. When the spring dynamometer pulls the wood block to do uniform linear motion on the horizontal plane, the magnitude of the pulling force is equal to the magnitude of the friction force, and the magnitude of the pulling force can be read from the spring dynamometer, thus measuring the friction force between the wood block and the horizontal plane.
Inquiry guidance
Inquiry guidance:
Trains with stalled engines will stop, swinging swings will stop, kicked football will stop, and moving objects will stop because of friction.
Friction produced by moving objects must meet the following three conditions: 1. Objects should contact and squeeze each other; 2. The contact surface should be rough; 3. There should be a trend of relative motion or relative motion between two objects. Three conditions are indispensable.
The point of action of friction is on the contact surface, and the direction is opposite to the direction of relative motion of objects. From the three elements of force, we can know that friction not only has the point and direction of action, but also has the magnitude.
Question: What factors are related to the magnitude of friction?
Guess 1: the magnitude of friction may be related to the pressure on the contact surface.
Conjecture 2: The magnitude of friction may be related to the roughness of the contact surface.
Conjecture 3: The magnitude of friction may be related to the size of the contact area between two objects that generate friction.
Query scheme:
Pull the wood block with a spring dynamometer at a uniform speed to make it slide along the long board, so as to measure the friction between the wood block and the long board; Change the weight placed on the block, thus changing the pressure between the block and the long board; Spread cotton cloth on the long board to change the roughness of the contact surface; Change the contact surface between the wood block and the long board, thus changing the contact area.
Query process:
1. Pull the block with a spring dynamometer at a uniform speed, and measure the friction between the block and the long board at this time: 0.7N
2. Add 50g weight to the wood block, and measure the friction between the wood block and the long board at this time: 0.8N
3. Add a weight of 200g to the wood block, and measure the friction between the wood block and the long board at this time:1.2n.
4. Spread the cotton cloth on the wooden board, and measure the friction between the wooden block and the long board at this time: 1.438+0N.
5. Speed up the pulley at a uniform speed, and measure the friction between the pulley and the long board at this time: 0.7N
6. Turn the block over so that the other side with smaller area contacts the long board, and measure the friction between the block and the long board at this time: 0.7N
Query conclusion:
1. The magnitude of friction is related to the pressure acting on the surface of an object. The greater the surface pressure, the greater the friction.
2. The magnitude of friction is related to the roughness of the contact surface. The rougher the contact surface, the greater the friction.
3. Friction has nothing to do with the contact area between objects.
4. The magnitude of friction has nothing to do with the speed of relative motion.