"Scientific Inquiry: Friction" Familiar and Unfamiliar Forces PPT Courseware 4

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"Scientific Inquiry: Friction" Familiar and Unfamiliar Forces PPT Courseware 4

1. When a bicycle slides on a level road, no matter how smooth the road surface is, it will gradually slow down and finally stop.

2. After the car brakes, the car will also stop slowly.

think:

People deal with friction all the time. Imagine what would people's lives be like without friction?

1. Sliding friction

The force that prevents the relative sliding of an object when an object slides on the surface of another object is called sliding friction.

Static friction: When an object is about to move, the force on the contact surface that hinders the movement of the object is called static friction.

Rolling friction: When an object is rolling, the force on the contact surface that hinders the movement of the object is called rolling friction.

1. When wiping the blackboard, the friction between the blackboard sassafras and the blackboard

2. When the bicycle is braking, the friction between the brake pad and the steel rim

3. When writing with a pen, the friction between the pen and the paper

4. The child slides down the slide, and the friction between the child and the slide

Thinking: What factors are related to sliding friction?

Scientific inquiry: What factors are related to sliding friction?

Conjecture 1: It may be related to the roughness of the contact surface

Conjecture 2: It may be related to the pressure between the contact surfaces

Conjecture 3: It may be related to the size of the contact surface

2. What factors are related to sliding friction?

Experimental conclusion: A large number of experiments have shown that the size of sliding friction is related to both the size of the pressure and the roughness of the contact surface. The greater the pressure, the greater the sliding friction; the rougher the contact surface, the greater the sliding friction.

In order to study the factors of sliding friction, a student conducted an experiment as shown in the figure.

(1) In the experiment, in order to make the indication of the spring scale equal to the sliding friction force on the wooden block, the wooden block should move _________ under the action of the tension of the spring scale.

(2) Figures A and B illustrate: _________ the greater the sliding friction

(3) Figures A and C illustrate: _________ the greater the sliding friction

(5) The above experiment adopted the ________ research method.

3. Summary

1. Sliding friction

The force that an object experiences when sliding on the surface of another object that prevents the relative sliding of the object

2. What factors are related to sliding friction?

The amount of pressure and the roughness of the contact surface

3. A physical method was used to explore which factors sliding friction is related to.

Control Variable

review

The size of the sliding friction force is related to both the size of the pressure and the roughness of the contact surface. The greater the pressure, the greater the sliding friction; the rougher the contact surface, the greater the sliding friction.

1. The following methods are used to reduce friction:

A In winter, sprinkle some fine sand on the icy road to make it easier for passers-by to walk.

B. Drop some oil on the rusty bicycle shaft and it will be easier to ride.

C When the rear wheels of a car get stuck in a mud puddle, the driver will find rocks to put under the wheels.

D. Gymnasts perform parallel bars and apply talc on their hands to prevent them from slipping off the bars.

2. Among the following life examples, the one that reduces friction is [ ]

A. Add lubricating oil to the car's rotating shaft

B． sole pattern

C. Sprinkle cinders on icy roads

D． When tug-of-war, hold on to the rope firmly

3. Among the following statements about the pros and cons of friction, the correct one is [ ]

A. When the locomotive starts, the friction between the locomotive wheels and the rails is beneficial friction.

B. In belt transmission, the friction between the belt and the pulley is harmful friction.

C. When riding a bicycle, the friction between the bicycle wheel and the axle is beneficial friction

D. When people walk, the friction between shoes and the ground is beneficial friction.

Analysis: When friction is used as power, it is beneficial friction, and when used as resistance, it is harmful friction.

In order to explore what factors are related to the size of sliding friction, Xiao Ming conducted a series of experiments. The following are some experimental steps:

The first time: Place the wooden block horizontally on the long wooden board, use a spring dynamometer to pull the wooden block horizontally to make a uniform linear motion (as shown in Figure A), read the reading of the spring dynamometer, and record it in the following table:

The second time: Place the wooden block on its side on the long wooden board, pull the wooden block in the same way (as shown in Figure B), and record the corresponding number;

The third time: Stack two identical wooden blocks together and lay them flat on a long wooden board, then use the same method to pull the wooden blocks (as shown in Figure C), and record the corresponding numbers.

(1) Please help Xiao Ming fill in the data in the form;

(2) Comparing the first and second experimental data, it can be found that ____________________;

(3) Comparing the first and third experimental data, we can draw the conclusion:_______________

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Update Time: 2024-10-21

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