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Engineering ToolBox > Acceleration of Gravity and Newtons Second Law
Acceleration of gravity is one of the most used physical constants - most known from
"Change of motion is proportional to the force applied, and take place along the straight line the force acts."
Newton's second law for the gravity force - weight - can be expressed as
F = m g (1)
where
F = force (weight)
m = mass
g = acceleration of gravity
The force caused by gravity - g - is called weight. Note! Mass - m - is a property.
The acceleration of gravity can be observed by measuring the change velocity of a free falling object:
g = dv / dt (2)
where
dv = change in velocity
dt = change in time
If we drop an object we will observe that it will accelerate to a speed of 9,81 m/s or 32,174 ft/s in one second.
g = 9.81 m/s2
g = 32.174 ft/s2
The velocity of a free falling object can be expressed as:
v = g t (3)
where
v = velocity
The distance traveled by a free falling object can be expressed as:
s = 1/2 g t2 (4)
where
s = distance traveled by the object
The velocity and distance traveled by a free falling object:
| Time (s) | Velocity | Distance | ||
| m/s | ft/s | m | ft | |
| 1 | 9.8 | 32.2 | 4.9 | 16.1 |
| 2 | 19.6 | 64.3 | 19.6 | 64.3 |
| 3 | 29.4 | 96.5 | 44.1 | 144.8 |
| 4 | 39.2 | 128.7 | 78.5 | 257.4 |
| 5 | 49.1 | 160.9 | 122.6 | 402.2 |
| 6 | 58.9 | 193.0 | 176.6 | 579.1 |
| 7 | 68.7 | 225.2 | 240.3 | 788.3 |
| 8 | 78.5 | 257.4 | 313.9 | 1,029.6 |
| 9 | 88.3 | 289.6 | 397.3 | 1,303.0 |
| 10 | 98.1 | 321.7 | 490.5 | 1,608.7 |
Note! The velocity is achieved without any aero-dynamical resistance (vacuum). Obviously the air resistance will be significant for increasing velocities.
"Every body continues in a state of rest or in uniform motion in a straight line, until it is compelled by a force to change its state of rest or motion."
"To every action there is always an equal reaction - if a force acts to change the state of motion of a body, the body offers a resistance equal and directly opposite to the force."