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Example Question #1 : Newton's Second Law
Which of the following best illustrates Newton's Second Law?
A ball is rolled across a table and does not stop until it hits an area with friction
If an object is not accelerating, then the net force on it is zero
As a hammer hits a nail, the nail also exerts a force on the hammer
When two cymbals collide, some kinetic energy is converted into sound
If an object is not accelerating, then the net force on it is zero
Newton's Second Law is best represented as an equation, in which the product of mass and acceleration is equal to net force:
By this principle, if there is zero acceleration, then the force must also be zero.
A non-zero acceleration must be present if there is a non-zero net force.
Example Question #1 : Motion And Mechanics
Which of the following is the best example of Newton's Third Law?
When two objects collide, the total initial and total final momentum will be equal
A spinning top will not fall unless there is friction with the surface on which it spins
If an object's weight rests on the floor, then the floor will exert a normal force on the object
The force of being hit by an object is determined by its mass and acceleration
If an object's weight rests on the floor, then the floor will exert a normal force on the object
Newton's Third Law states that for every action there is an equal and opposite reaction. In other words, a force will act in equal and opposite directions on the two objects involved.
Weight and normal force are a specific example of this principle. Acceleration due to gravity creates a downward force, known as weight. This force, however, results in zero downward acceleration when the object is resting on a surface (a book does not fall through a table, for example). For the forces to be in equilibrium, there must be a counteracting upward force. This is known as the normal force, which is equal and opposite to the weight of the object. While weight pulls the object down, normal force pushes it up to create equilibrium.
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