Question 14
Give reasons for the answers to each of the following questions: a) Can a normal force be horizontal? b)
Can a normal force be directed vertically downward? c) Consider a tennis ball in contact with a
stationary floor and with nothing else. Can the normal force be different in magnitude from the
gravitational force exerted on the ball? d) Can the force exerted by the floor on the ball be different in
magnitude from the force the ball exerts on the floor?
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a) Can a normal force be horizontal?
To determine if a normal force can be horizontal, we need to understand what a normal force actually is. The normal force is the force exerted by a surface to support the weight of an object resting on it. It acts perpendicular to the surface at the point of contact.
In most cases, a normal force is directed vertically upwards, opposing the downward force of gravity. This is because objects typically rest on horizontal surfaces, and the normal force is required to balance the weight of the object.
However, there can be situations where a normal force can have a horizontal component. One example is when an object is on an inclined plane. In such cases, the component of the normal force parallel to the plane can be horizontal.
b) Can a normal force be directed vertically downward?
Normally, the direction of the normal force is perpendicular to the surface it acts upon, and it opposes the force of gravity. Therefore, a normal force is typically directed vertically upwards to counteract the downward pull of gravity.
In exceptional cases, a normal force can be directed vertically downward. One instance is when an object is in freefall or accelerating downwards. In such scenarios, the normal force still exists, but it acts in the opposite direction to the usual convention.
c) Consider a tennis ball in contact with a stationary floor and with nothing else. Can the normal force be different in magnitude from the gravitational force exerted on the ball?
In this scenario, the weight of the tennis ball creates a gravitational force pulling it downwards. The normal force, exerted by the floor, acts in the opposite direction. According to Newton's third law of motion, the magnitude of the normal force is equal to the magnitude of the gravitational force.
Both the normal force and the gravitational force have the same magnitude but act in opposite directions. This is because the ball is not accelerating vertically and is in equilibrium. If there were any difference in magnitude between them, the ball would accelerate upwards or downwards.
d) Can the force exerted by the floor on the ball be different in magnitude from the force the ball exerts on the floor?
According to Newton's third law of motion, whenever a force is exerted on an object, an equal and opposite force is exerted by the object on the source of the force. This law applies to the interaction between the tennis ball and the floor.
Therefore, the force exerted by the floor on the ball is equal in magnitude but opposite in direction to the force exerted by the ball on the floor. Both forces have the same magnitude as they are part of an action-reaction pair.