Investigating the Factors Which Affect the Motion of a Trolley Down an Inclined Plane

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Science Coursework

INVESTIGATING THE FACTORS WHICH AFFECT THE MOTION OF A TROLLEY DOWN AN INCLINED PLANE

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The aim of this investigation is to show how the height of a ramp affects the speed at which a dynamics trolley rolls down it. I also hope to investigate whether the mass of the trolley has any affect on its speed.

Theory

A force is a pull or push. If you wanted to exert a force on something you could, for example, push it, pull it, twist it, or squeeze it. Five important kinds of force are:

1.        Gravitational Forces caused by the pull of the earth on objects

2.        Frictional Forces try to stop things moving. They cause the friction or drag which stop objects slipping over each other or sliding past each other.

3.        Contact Forces are produced when two objects are pushed together. The contact force from the starting block pushes a sprinter away at the start if a race.

4.        Magnetic Forces act on magnetic materials. The magnetic strip in a magnetic door catch pulls the door to the frame and keeps the door closed.

5.        Electric Forces act between electric charges. Electric forces (static) sometimes make your hair cling to a plastic comb.

Forces 1 and two will be a major factor when we investigate which factors affect the rate of the trolley's movement.

Sir Isaac Newton’s laws of motion are directly relevant to this investigation, they help to explain why a dynamics trolley would move, stop, accelerate, or decelerate.

1.        Newton's First Law: "Every body continues in its state of rest, or of uniform motion in a right line, unless it is compelled to change that state by forces impressed on it."

If you roll a stone over a flat icy, surface it seems to move on and on because there is so little friction. If we could reduce friction and air resistance (drag) to zero, the stone would go on rolling forever. In practice, most moving objects slow down because of external frictional forces act on them. If, however, the frictional forces of the moving object are just balanced by other forces causing the object to move, then the object will continue to move with constant velocity.

2.        Newton's Second Law: "The change of motion is proportional to the motive force impressed; and is made in the direction of the right line in which that force is impressed."

Newton’s first law is concerned with objects at rest or those moving at a constant speed. His second law is concerned with the motion of accelerating and decelerating objects. When accurate investigations are made, the results show that the acceleration doubles when the force doubles and acceleration trebles when the force trebles, etc…this means that the acceleration is proportional to the force applied. i.e.

Equation One

Acceleration ∞ force

In symbols this is also written as:

a ∞ F  

From experience, we also know that a small car is easier to push and accelerate than a large van. Accurate experiments show that if you push double the mass, with the same force, the acceleration is only half what it was. These results can be summarized by saying that acceleration is inversely proportional to mass.

Equation Two

Acceleration ∞ 1

                   

                       Mass

Or:

   a   ∞ 1

        M           

Equation Three

Equations 1 and 2 can be combined to give:

    a ∞ F

      m

Or:

F ∞ m x a

Equation Three is the mathematical form of Newton’s second law of motion. The equation for Newton’s second law of motion can also be written as:

F = k x m x a

Where k is constant. However, the unit of force (one Newton) was chosen sop that k equals one, so we can write

Equation Four:

Force = mass x acceleration

F = m x a

Using equation 4,

One Newton is the force, which gives a mass of 1kg and an acceleration of one m/s squared. When using equation four,

        F must be in Newton’s

        m must be in kilograms

        a must be metres per second

3.         Newton's Third Law: "To every action there is always opposed an equal reaction: or, the mutual actions of two bodies upon each other are always equal, and directed to contrary parts." or more commonly "For every action force, there is an equal and opposite reaction force".

Newton’s third law is not directly relevant to my investigation however, it helps me to understand principles of forces, it explains what happens when objects push against each other and collide.

On a flat plain a dynamics trolley has three forces acting upon it weight, friction and air resistance however as demonstrated in Newton’s first law it will stay motionless unless a force is applied. (See diagram)

For the investigation, it is important to understand the difference between weight and mass, as weight is one of the forces acting upon the dynamics trolley:

Weight is the force of gravity on an object, measured in Newton’s (N).

Mass is the amount of matter in an object, measured in kilograms (kg).

WEIGHT IS A FORCE

Frictional forces also act upon the trolley; they are the forces, which prevent motion. These forces prevent an object moving over a surface or through a fluid. Friction occurs when the molecules of one object get very close to the molecules of another surface. The forces of attraction between the molecules must be overcome in order to move one surface over another. Friction has three major effects:

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i)        It prevents objects moving or slows them down;

ii)        It produces heat when two objects rub against each other.

iii)        It wears things out as surfaces rub together.

In our investigation we hope to reduce friction by using a dynamic trolley, however this is not 100% possible. However, friction can be reduced by the use of:

-        Bearings,

-        Lubrication,

-        Streamlining.

Bearings and lubrication are used to reduce friction between a wheel and its axle. The ball bearings reduce the area of contact between the moving surfaces. The oil between the bearings, wheel and axle acts as a lubricant by separating the moving ...

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