The shape, motion state, size and direction of the interactive object are in direct proportion to the earth, G=mg, the relative motion pressure vertically downward, the roughness of the contact surface F 1L 1=F2L2, and it is labor-saving and laborious. Changing the direction of force cannot change the direction of force.

Integration, expansion and innovation

[for training]

1.D

2. The title is abbreviated

(1) ratio

(2)①4.5 ② 1.8 ③ 1, ② The ratio of the elongation length of Xiaoming rubber band to each pulling force remains unchanged (or the pulling force is expanded several times, so is the elongation length of rubber band).

3.90 150

4.B

5. the topic is abbreviated.

(1) The left level can eliminate the influence of the self-weight of the lever.

(2) The unreasonable conclusion of f1l1= f2l2 is accidental (the conclusion is not universal).

(3) the influence of the self-weight of the lever

6.C 7。 B