People's Education Press High School Physics Required Course Book 1: Force and Deformation

Force is an interaction between objectsinteraction, and cannot exist independently of objects. The effects of force manifest in two ways: first, changing an object'smotion state(speed or direction), and second, causing an object to undergodeformation.

Figure: Laser Reflection Method Demonstrating Invisible Deformation

Classification and Limits of Deformation

Elastic Deformation (elastic deformation): Refers to deformation that an object can recover from after external forces are removed. This is the physical basis for elastic force generation.
Elastic Limit (elastic limit): The maximum extent to which an object can maintain its ability to return to its original shape. If external forces exceed this limit, the object will undergo permanent deformation or even damage.

The Science of Perception: Amplification Method

Not all deformations can be directly observed by the naked eye. In physics, theamplification methodis commonly used to prove the existence of small deformations. For example, when you press a rigid lab table, the small angular deviation caused by deformation is magnified through multiple reflections of laser beams between two plane mirrors, resulting in a clearly visible displacement on a distant screen.

QUESTION 1

Provide specific examples to illustrate: (1) how force can change an object's motion state or cause deformation; (2) that every force has both a source object and a receiving object.

Example 1: Molding clay; Example 2: Pushing a cart, where your hand is the force source.

Only gravity does not require a source object.

QUESTION 2

[Short Answer] Provide specific examples to illustrate: (1) how force can change an object's motion state or cause deformation; (2) that every force has both a source object and a receiving object.

Click to view the reference answer

QUESTION 3

[Short Answer] [Image: A truck carrying a barrel] As shown in the figure, a barrel rests on a car parked on a horizontal surface. How many pairs of action-reaction forces exist among the barrel, car, and Earth? Which forces act on the barrel?

4 pairs of forces; the barrel experiences gravity and support force from the car.

3 pairs of forces; the barrel only experiences gravity.

QUESTION 4

An air conditioner unit is fixed with two triangular brackets (as shown in Figure 3-6), with a weight of 200 N. The horizontal beam AO is level, and the inclined beam BO makes an angle of $37^{ ext{°}}$ with the horizontal beam. Calculate the tensile force $F_{AO}$ exerted by the horizontal beam on point O and the compressive force $F_{BO}$ exerted by the inclined beam on point O (assuming one bracket bears the entire weight).

$F_{BO} \approx 333.33\text{N}, F_{AO} \approx 266.67\text{N}$

$F_{BO} = 200\text{N}, F_{AO} = 200\text{N}$

QUESTION 5

If the inclined beam of the above air conditioner bracket is slightly lengthened while keeping point O fixed and the horizontal beam still level, how will the magnitudes of the forces exerted by the horizontal and inclined beams on point O change?

Both decrease

Both increase

Tensile force in the horizontal beam increases, compressive force in the inclined beam decreases