Topic content:
The following statement is correct ()
A. The gravity on the object must be vertically downward, and the center of gravity of the object may not be on the object
B. Only very small objects can be regarded as particles, while large objects cannot be regarded as particles
C. If two objects move at the same speed, the displacement that two objects pass through in the same time must be the same
D. The object has inertia when moving at a uniform speed, and loses inertia when moving at variable speed under the action of external force
Best answer:
A、 The direction of gravity is always vertical and downward, and the center of gravity of the object is not necessarily on the object, not a hollow ball, so A is correct;
B、 Whether an object can be regarded as a particle depends on whether the size of the object can be ignored in the study; Small objects may not be reduced to points, for example, when studying the internal structure of electrons, electrons cannot be reduced to particles; So B is wrong;
C、 If two objects move at the same speed, it means that the speed is equal, but the direction is not necessarily the same, then the two objects must pass the same distance in the same time, but the displacement direction is not necessarily the same, so C is wrong;
D、 The only measure of inertia is the mass, which has nothing to do with whether the force is applied, so D is wrong;
Therefore: A
Answer analysis:
There is no explanation for this question
Test core:
Center of gravity: The point where gravity acts on an object is called the center of gravity.
① For objects with uniform mass distribution, the position of the center of gravity is only related to the shape of the object (the center of gravity with regular shape is on their geometric center);
② For an object with uneven mass distribution, the position of the center of gravity is related not only to the shape of the object, but also to the mass distribution inside the object;
③ The center of gravity can be on or outside the object.
