Mammoth Memory

Newton's second law – Examples

In the following examples of Newton's second law we will use the formula `F=ma` and if we expand on this we get
`F(n\e\t\ \f\o\r\c\e\ \o\n\ \o\b\j\e\c\t)=m\a\s\s\ \o\f\ \o\b\j\e\c\t\xx\a\c\c\e\l\e\r\a\t\i\o\n`

To help you understand the words in this formula a little more it may help to think of them as follows:

        Force  `=`  Push or pull
  Acceleration  `=`  Move
  Mass  `=`  Weight


Be very careful with these ideas because there is a lot more meaning behind each of these words but as a quick rule of thumb, it may help jolt a memory.


Example 1

If you think of acceleration as movement, then:

"The greater the mass of the object, the more force needed to make it accelerate"

can be read as:

"The greater the mass of the object the more force is needed to make it move."

A large mass requires more force to move it than a small mass does.

Objects with a greater mass have more inertia. It takes more force to change their motion. A 400kg rock is a lot harder to move than a 40kg rock. 


Example 2

Use  `F=ma`

Twice the mass requires twice the force to produce the same acceleration.

It will take twice the amount of force to accelerate the wagon with 20kg as the wagon with 10kg. But in order to make an object accelerate or move you have to apply a force.


Example 3

A baseball will travel a greater distance than a bowling ball when both are hit with the same force.

Because the mass of each ball is different, each ball will travel a different distance and at a different speed when it is hit with the same force.


Example 4

One hand pushing one brick.

Force of hand accelerates the brick

Two hands pushing one brick.

Twice as much force produces twice as much acceleration.

Two hands pushing two bricks.

Twice the force on twice the mass gives the same acceleration.


Example 5

A golf ball will accelerate must faster than a truck when the same force is applied to each.


`F=m1xxa` Large acceleration (large motion)

`F=m2xxa` Small acceleration (small motion)

How much an object accelerates depends on the mass of the object and how much force is applied to it. 

The effect of a 10 Newton force on a golf ball would be much greater than that same force acting on a truck.


Example 6

If 10 Newtons act in each direction on an object the net force is zero.


If two 10N forces act on an object in the same direction the net force is 20N.


Unbalanced forces cause acceleration.

If 10N acts in one direction on an object and 8N in the opposite direction the net force is 2N.


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