Are there any good experiments on two-force balance in junior high school physics?

Experiment to study the conditions for the balance of two forces.

Put the lines tied to the two diagonal corners of the card across the pulleys on the left and right brackets (Textbook P88? Figure 10-9), as shown in the picture above.

(1) Step 1: Hang the hook code on the end of the line. The two forces acting on the small card are in opposite directions and on the same straight line. See under what circumstances the card is in balance. state? Under what circumstances can a card

not be balanced? (As shown in the picture below)

(2) Step 2: Turn the small card at an angle so that the two pulling forces on the small card are not in a straight line, but are equal in magnitude and opposite in direction. Will the card remain balanced after letting go?

(3) The card is in a balanced state. Use scissors to cut the card in half. The hook code and half of the card will fall to both sides, indicating that the two must act on the same object.

(4) The teacher asked a question: Observe, analyze and summarize what conditions are met for the board to be stationary? Students discuss and summarize.

[Summary] The condition for the balance of two forces is: the two forces acting on the same object are equal in magnitude, opposite in direction, and act on the same straight line. "Eight-character oral judgment" has the same body, equal value, reverse and *** line.