Q4E Case Study 25 – Gravity ‘ Estimating the Magnitude’
Proposed subject useage
Sports Science / Mathematics / Physics (A/AS level / Degree Yr 1/2)
Gravity acts on any object with mass, and causes said object to be accelerated towards the centre of the Earth at a constant rate, producing the force known as weight. Acting purely in a vertical direction, gravity accelerates objects downwards, and if this object is not in contact with the ground (i.e. is a projectile), then its vertical velocity increases in a downward direction. When in contact with the ground, a reaction force is exerted to equal the force produced due to the acceleration of gravity (using the principles of both Newton’s 2nd Law of acceleration (F=ma), and Newton’s 3rd Law of Action Reaction). However, when an object is a projectile, the only other force exerted is that of the resistive force of air resistance. For this particular case study, air resistance was ignored as its magnitude was considered to have negligible affects on the flight of the ball. Therefore the acceleration of the ball was considered a direct cause of the affects of gravity.
At ground level on the surface of the Earth, gravity is widely accepted to have a value of -9.81 m∙s-2. For this case study, this was the value to which comparisons were made. (It is important to note that this negative sign does not mean that the object is slowing down (decelerating), but indicates the direction in which gravity acts. When using the convention of positive travel being upwards, a negative acceleration just means that an object is accelerating in a negative direction, i.e. accelerating downwards)