# newtons second law

## direct and inverse relationships

Newtons second law shows that there is a direct relationship between force and acceleration. The greater the force that is applied to an object of a given mass, the more the object will accelerate. For example, doubling the force on the object doubles its acceleration. The relationship between mass and acceleration is different. It is an inverse relationship. In an inverse relationship, when one variable increases, the other variable decreases. The greater the mass of an object, the less it will accelerate when a given force is applied. For example, doubling the mass of an object results in only half as much acceleration for the same amount of force. Q: Tony has greater mass than the other two boys he is racing (pictured in the opening image). How will this affect his acceleration around the track? A: Tonys greater mass will result in less acceleration for the same amount of force.

## force mass and acceleration

Whenever an object speeds up, slows down, or changes direction, it accelerates. Acceleration occurs whenever an unbalanced force acts on an object. Two factors affect the acceleration of an object: the net force acting on the object and the objects mass. Newtons second law of motion describes how force and mass affect acceleration. The law states that the acceleration of an object equals the net force acting on the object divided by the objects mass. This can be represented by the equation: Acceleration = or a = Net force Mass F m Q: While Tony races along on his rollerblades, what net force is acting on the skates? A: Tony exerts a backward force against the ground, as you can see in the Figure 1.1, first with one skate and then with the other. This force pushes him forward. Although friction partly counters the forward motion of the skates, it is weaker than the force Tony exerts. Therefore, there is a net forward force on the skates.

## instructional diagrams

No diagram descriptions associated with this lesson

## questions

acceleration occurs whenever an object is acted on by an unbalanced force.

``````-->  a. true

b. false
``````

factors that affect the acceleration of an object include the

``````a) net force acting on the object.

b) objects speed.

c) objects mass.

-->  d) two of the above
``````

there is a direct relationship between acceleration and mass.

``````a. true

-->  b. false
``````

increasing the force acting on an object increases its acceleration.

``````-->  a. true

b. false
``````

if the net force acting on an object increases by 50 percent, then the acceleration of the object will

``````a) decrease by 50 percent.

b) increase by 100 percent.

c) stay the same.

-->  d) none of the above
``````

which equation shows the relationships among acceleration, mass, and net force?

``````a) acceleration = net force x mass

-->  b) acceleration =- net force/mass

c) acceleration = mass/net force

d) none of the above
``````

## diagram questions

No diagram questions associated with this lesson