Inertia Investigation

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Plan

To give myself a greater knowledge of the physics involved in this

experiment I have carried out background research. The area that my

experiment investigates is the affect of changing the surface area of an

object of the same mass falling from a specified height and how it changes

air resistance. Several factors of physics will affect my experiment and I

have researched these factors and I will show my findings in this first

section of my experiment.

Firstly Newton’s first law of motion states that an object will remain at a

constant velocity or at rest unless an unbalanced force acts upon it. When

an object is falling it is accelerating, unless it reaches terminal velocity

which I will explain later, so there must be an unbalanced force acting

upon it pulling it downwards. This downwards force is called gravity. The

force of gravity is determined by multiplying an objects mass in Kg by

9.81 as the gravitational force on earth is 9.81N/Kg. However when an

object is falling in a vacuum without air resistance in free fall there is still

another factor that must be taken into account this is inertia.

Inertia = the resistance an object has, to a change in its movement.

This means that the greater an objects mass the more force it will take to

change its movement as it will have a higher inertia and resistance to

another force changing its movement.

The force of inertia then cancels the affect of mass on the acceleration of

an object due to gravity. If an objects mass is 10Kg it will have a

downward force of 10 x 9.8 = 98N acting on it. If an object has a mass of

1 Kg it will have a force of 9.8N acting on it. But because acceleration =

force/mass the acceleration of these objects will be the same.

Book 1                                                                Book 2

Mass=10Kg                                                        Mass=1Kg

100N                                                                10N

          A= 100/10                                                

          A=10m/s2                                                A=10/1

                                                                        A=10m/s2

This means that on earth in a vacuum where all other forces are equal and

balanced two different mass’s will fall with the same acceleration.

However in a normal environment this is not always true as there are other

forces that will be acting on the object as it will be falling. Air resistance is

the main force that will act upon an object falling through the air. Air

resistance is a resistive force, this means that it resists the motion of

another force, for example gravity, when an object is falling or the forward

speed of a plane, a resistive force can be made big if it is acting on a larger

surface area, or made small if it is acting on a small surface area. Air

resistance occurs because as an object passes through the air it hits air

molecules and has to force them out of the way, this requires energy as

these molecules, although very small, have their own inertia and will resist

the actions of an outside force to a certain extent. Because of this the

bigger the surface area that is in contact with air molecules, in the direction

the object is moving, the greater the resistive force as there will be more

molecules that need to be moved and so a greater force of inertia. So

Object 1 will encounter less resistance than Object 2 even though they

have the same mass.

 

Mass = X                                                                      Mass = X  

     

As you can see the bottom of the object on the left is in contact with more

air molecules than the one on the right. Even though they have the same

gravitational force pulling them down the one on the left has a greater

force of air resistance acting upon it so it will have a slower acceleration.

There are also other factors that may affect the amount of air resistance on

an object, the density of the air, as this changes the amount of molecules

which will be in the way of the falling object, but this is not relevant to my

investigation as it will be conducted at ground level. The other factor is the

speed at which an object falls. If the object is falling faster it will hit more

air molecules per second as it will be passing through more air in 1

second. This means that it will have to move more air molecules out of the

way and the air resistance force will be greater. Because of this objects of

different gravitational force have different terminal  velocities. For example

even though 2 objects with different masses will accelerate at the same

speed because of inertia if they have the same amount of air resistance the

one with the lower mass and gravitational force will reach terminal velocity

and stop accelerating first, meaning that it will travel at a lower speed than

the object with high mass. For example if 2 objects have masses of 10kg

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and 1kg respectively they will have gravitational forces of 100N and 10N,

they will begin to accelerate at the same speed  when air resistance is 0N,

but if both encounter the same air resistance the object with the smaller

mass will slow more quickly whereas the larger object will slow more

slowly as you can see from these two tables below which shows the

resultant downward force which is the gravitational force minus air

resistance and acceleration.

Object with mass of 10Kg

Object with mass of 1Kg

Resultant Force in ...

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