# Factors Affecting the Speed of a Car after Freewheeling down a Slope

Factors Affecting the Speed of a Car after Freewheeling down a Slope

Background Knowledge

#### A moving object covers a particular distance in a particular time. This is called the Speed of the object and is expressed as meters/second i.e. the distance covered in meters in one second. It is a Scalar quantity as it only has magnitude. If however the same speed is expressed with the object moving in a particular direction e.g. due north, it will be called the Velocity of the object. It again is expressed as meters/second but having both magnitude and direction it is a Vector quantity.

##### Newton described that an object that is stationary will stay stationary until a force is applied to it and an object that is in motion will stay in motion in a straight line until it is acted upon by a force. This is Newton’s First Law of Motion.

Average Velocity = Displacement taken place (m)

(m/s)                        Time taken (s)

Force is a push or a pull, which can make an object start moving when it is stationary, or change its shape or its direction of motion. It is measured in Newton (N).

When an external force acts upon a moving object it changes its velocity. The rate at which this velocity is changed is called acceleration  (if the velocity is increased) or deceleration (if the velocity is decreased by an opposing force). This is the Second Law of Motion. And acceleration is expressed in m/s2.

Acceleration = Change in Velocity (m/s)

(m/s2 )                   Time taken (s)

It is the property of matter that it opposes any change in an object’s fixed position. This is called Inertia. The greater the mass of an object the greater will be the force of Inertia. This indicates that to make an object move from its stationary position, it will take a stronger force if the mass of the object is more as compared to the force needed to move a lighter object with less mass. Similarly the force needed to change the velocity (acceleration) of a moving object will depend upon it mass. The stronger the force applied the more will the acceleration be. The more the mass of an object, the less will the acceleration of the object when the same amount of force is applied.

So one can express that acceleration (a) is directly proportional to the Force (F) applied to an object and inversely proportional to the mass (m) of the object.

One Newton is the force that gives a mass of 1Kg an acceleration of 1meter/sec2.

1N=1Kgm/sec2

A moving object keeps moving due to a force called Kinetic Energy. Energy can neither be created nor destroyed (Law of Conservation of energy). It merely changes from one form to another. The energy present in a moving object is called Kinetic energy.  It is expressed as:

KE = ½ mv2

Where KE is the Kinetic energy, m is the mass of the object in Kg and v is the velocity of the moving body. This indicates that higher the velocity of a moving object, the higher is the kinetic energy in the object.

Before an object can start to move from a stationary position, it either has to possess some energy inside it or has to be forced to start moving. A body that has energy due to its position or condition is called the Potential Energy. An object above the surface of the earth is considered to have Gravitational Potential Energy. This is when an object gains energy by being lifted to a height above the ground. In my experiment I will be placing a trolley on a ramp at a height above the surface of the earth. It is the potential energy in the trolley that let it come down the slope when it is let go.

Work done by force = force x height

= mass x gravity x height

Mass is measured in Kg.   Gravity in Newton/kg and height in meters

This indicates that if the mass of the object is increased and the height is kept constant and with the force of gravity being constant, it will take more force to place the object to a height and the object would hold more potential energy. Similarly, if the height is increased and the mass of the object is kept constant, more potential energy will be held by the object at higher level than at lower levels.

When an object is realised from a height, it accelerates down the slope due to its Gravitational potential being converted into Kinetic energy (called Energy Conversion), until it reaches a flat surface when it continues to move (First Law of Motion) at a constant velocity until it is stopped mechanically or by friction due to its contact with the surface it is moving on.

At any one time the forces acting on the trolley are:

• The force of gravity pulling the trolley towards the earth.
• Opposing force from the ramp pushing the trolley upwards
• Kinetic energy making the trolley go down the runway
• The force of air resistance and friction opposing the run of the trolley

FORCES KEEPING THE TROLLEY ON THE RUNWAY

FORCE MOVING THE TROLLEY DOWN THE RAMP

The ticker timer and tape

The ticker timer has a small metal ball that vibrates 50 times in one second. The gap between each dot on the ticker tape is therefore one fiftieth of a second. To measure the time taken for your trolley to freewheel down the ramp, you would have to count the number of dots starting form the regular intervals. The number of dots is then divided by 50 and the answer would be the time taken. This can then be used in the speed equation, v=s/t.

Plan

There are some possible factors that can be varied for the preliminary experiment:

1. The height of the runway- the larger the height of the runway, the more the gravitational pull on the trolley. This means the trolley will move with a greater speed at a higher gradient than at a lower one.
2. Length of the runway- the longer the runway, the more will be the acceleration of the trolley as it will have a greater time to travel on ...