What is Gravity?
Source: http://eschooltoday.com/science/forces/what-is-gravity.html
It’s quite simply the force two objects exert on each other. The extent of the force depends on how massive
the bodies are and also the distance which separates them.
This equation summarises the explanation above into a mathematical concept. G is
a gravitational constant equal to approximately 6.67 X 10
-11
m
3
kg
-1
s
-2
. As far as this
document is concerned, that is all we need to know about that constant since we
don’t explore it any further.
Using the information you now know, are you able to deduce what each of the letters represent in the equation?
F → the force due to gravity
G → Gravitational constant (6.67 X 10
-11
m
3
kg
-1
s
-2
)
m
1
→ the mass of one of the objects
m
2
→ the mass of the other object
r → the distance between the two objects (Note: you have to square this value in the equation)
When you jump, the Earth’s gravitational pull causes you to come back down; this is a fairly obvious idea we
grasp since an early age. Using the idea of ‘Every force has an opposite and equal force’ in this situation, we
can gather that when the Earth exerts a force on you, you actually exert the same amount of force back. It
seems ridiculous even thinking about this but it is in fact, true. Given that the Earth weighs 5.97 X 10
24
, calculate
the force of gravity if you were to jump 0.5m.
What is Acceleration?
Acceleration is the rate at which the velocity changes. In other words it is equal to the change in speed divided
by the time it takes to do so. Acceleration (and velocity) is a vector quantity, meaning it has magnitude as well
as direction. The magnitude consists of size and length but all three are equally important. For example,
assuming upwards is the positive value, an object falling due to gravity has a negative acceleration.
Just to build up on that idea, if a ball has as acceleration of 2 ms
-2
whilst being thrown up and it accelerates at
2 ms
-2
on its way down, too – it can be said that the ball has a -2 ms
-2
when it’s falling. If you take upwards as
the positive direction, then the ball is said to accelerate when thrown up and it is said to decelerate when it’s
falling. Strictly speaking, deceleration is known as negate acceleration. Hence, if the object is speeding up, it
has positive acceleration and it has negative acceleration if it’s slowing down.
Earth’s gravity provides acceleration at a rate of approximately 9.81 ms
-2
when an object falls. The acceleration
due to gravity is often referred to as the little g, as the big G is occupied by the gravitational constant mentioned
above.
The Engduino has the capability of capturing acceleration of values up to ±2g, twice that of the little g value.
Also, it can take measurements from all three dimensions. The other tutorials go into more detail about the
specific functionalities and the coding aspect.
The acceleration values from all three dimensions are returned by the
Engduino and stored in an array. All values are given in terms of g. The
values we are given lie in the x, y and z axis. Using this information, we can
find further information about the acceleration such as magnitude of
direction in any given direction.
If the value of z was 1, then we know that the Engduino is accelerating
upwards at 9.81 ms
-2
.
When at rest, the x, y and z values usually read at 0, 0 and -1 respectively. Are you able to explain why this is
the case?
The -1 z value tells us that gravity is acting on the Engduino and it is acting in the downward direction.
If you are only interested in the value of the acceleration and not the direction, then this can be determined
with a few calculations. As the acceleration values are known for all three dimensions, we can work out the
magnitude using the following equation:
Acceleration (magnitude) = √𝑥
2
+ 𝑦
2
+ 𝑧
2
