Gravitational force

Storyboard

Gravitational force is defined as the gravitational mass multiplied by the gravitational acceleration.The gravitational acceleration depends on the planet or moon being considered. While on Earth, the gravitational acceleration $g$ is 9.8 m/s², on the Moon, it's 1.625 m/s².

>Model

ID:(1413, 0)



Inertial and gravitational mass equality

Description

The gravitational mass m_g and the inertial mass m_i are empirically identical, so the acceleration of a body in the gravitational field does not depend on the mass of the object.

This was shown by the astronauts in Apollo 15. The first part contains the original video, the second a Hollywood type version.

ID:(11026, 0)



Gravitational force

Model

Gravitational force is defined as the gravitational mass multiplied by the gravitational acceleration. The gravitational acceleration depends on the planet or moon being considered. While on Earth, the gravitational acceleration $g$ is 9.8 m/s², on the Moon, it's 1.625 m/s².

Variables

Symbol
Text
Variable
Value
Units
Calculate
MKS Value
MKS Units
$a_0$
a_0
Constant Acceleration
m/s^2
$F$
F
Force with constant mass
N
$F_g$
F_g
Gravitational Force
N
$m_g$
m_g
Gravitational mass
kg
$m_i$
m_i
Inertial Mass
kg
$v_0$
v_0
Initial Speed
m/s
$s$
s
Position
m
$v$
v
Speed
m/s
$t_0$
t_0
Start Time
s
$s_0$
s_0
Starting position
m
$t$
t
Time
s

Calculations


First, select the equation:   to ,  then, select the variable:   to 

Symbol
Equation
Solved
Translated

Calculations

Symbol
Equation
Solved
Translated

 Variable   Given   Calculate   Target :   Equation   To be used



Equations

In the case where the constant Acceleration ($a_0$) equals the mean Acceleration ($\bar{a}$), it will be equal to

$ a_0 = \bar{a} $

.

Therefore, considering the speed Diference ($\Delta v$) as

$ dv \equiv v - v_0 $



and the time elapsed ($\Delta t$) as

$ \Delta t \equiv t - t_0 $

,

the equation for the constant Acceleration ($a_0$)

$ \bar{a} \equiv\displaystyle\frac{ \Delta v }{ \Delta t }$



can be written as

$a_0 = \bar{a} = \displaystyle\frac{\Delta v}{\Delta t} = \displaystyle\frac{v - v_0}{t - t_0}$



and by rearranging, we obtain

$ v = v_0 + a_0 ( t - t_0 )$

.

(ID 3156)

In the case of the constant Acceleration ($a_0$), the speed ($v$) as a function of the time ($t$) forms a straight line passing through the start Time ($t_0$) and the initial Speed ($v_0$), defined by the equation:

$ v = v_0 + a_0 ( t - t_0 )$



Since the distance traveled in a time ($\Delta s$) represents the area under the velocity-time curve, we can sum the contributions of the rectangle:

$v_0(t-t_0)$



and the triangle:

$\displaystyle\frac{1}{2}a_0(t-t_0)^2$



To obtain the distance traveled in a time ($\Delta s$) with the position ($s$) and the starting position ($s_0$), resulting in:

$ \Delta s = s - s_0 $



Therefore:

$ s = s_0 + v_0 ( t - t_0 )+\displaystyle\frac{1}{2} a_0 ( t - t_0 )^2$

(ID 3157)

If we solve for the time ($t$) and the start Time ($t_0$) in the equation of the speed ($v$), which depends on the initial Speed ($v_0$) and the constant Acceleration ($a_0$):

$ v = v_0 + a_0 ( t - t_0 )$



we get:

$t - t_0= \displaystyle\frac{v - v_0}{a_0}$



And when we substitute this into the equation of the position ($s$) with the starting position ($s_0$):

$ s = s_0 + v_0 ( t - t_0 )+\displaystyle\frac{1}{2} a_0 ( t - t_0 )^2$



we obtain an expression for the distance traveled as a function of velocity:

$ s = s_0 +\displaystyle\frac{ v ^2- v_0 ^2}{2 a_0 }$

(ID 3158)

Since the moment ($p$) is defined with the inertial Mass ($m_i$) and the speed ($v$),

$ p = m_i v $



If the inertial Mass ($m_i$) is equal to the initial mass ($m_0$), then we can derive the momentum with respect to time and obtain the force with constant mass ($F$):

$F=\displaystyle\frac{d}{dt}p=m_i\displaystyle\frac{d}{dt}v=m_ia$



Therefore, we conclude that

$ F = m_i a $

(ID 10975)


Examples


(ID 15844)


(ID 15417)

Gravitational mass is associated with what Newton defined as the law of gravitation, indicating the force that one body exerts on another.It should not be confused with inertial mass, which indicates the resistance a body generates when changing its state of motion. The latter is associated with the inertia experienced by bodies and is referred to as inertial mass.

(ID 14464)

The gravitational mass m_g and the inertial mass m_i are empirically identical, so the acceleration of a body in the gravitational field does not depend on the mass of the object.

This was shown by the astronauts in Apollo 15. The first part contains the original video, the second a Hollywood type version.

(ID 11026)


ID:(1413, 0)