Free fall

Содержание и основные понятия

Near the surface of the Earth, all bodies without air resistance fall at the same acceleration g. Vertical traffic is a private case of equal acceleration.
GEF · Grade 9
PIF · Baseline
Interactive model
free fall
acceleration g
vertical throw
Air resistance
01
The physical picture
What happens and what boundaries the model has.
Main message
Near the surface of the Earth, all bodies without air resistance fall at the same acceleration g. Vertical traffic is a private case of equal acceleration.
The body mass does not affect the acceleration of the free fall in the vacuum.
At the upper point of the drop, the velocity is instantaneously zero, but the acceleration remains equal to g.
Air resistance depends on shape, area and speed and can lead to a fixed speed.
How to reason
First, name the system and the interaction, then select the values, and only then write down the law. The formula works within the model's assumptions.
02
Laws and values
Symbols should be read as a relationship of values, not as a recipe for substitution.
v
=
v
0
−
g
t
v=v_0-gt
v
=
v
0
​
−
g
t
vertical speed
h
=
v
0
t
−
g
t
2
2
h=v_0t-\frac{gt^2}{2}
h
=
v
0
​
t
−
2
g
t
2
​
altitude
Review of the situation
A stone thrown upwards at a speed of 19.6 m/s, without resistance, rises approximately 2 s and reaches a height of 19.6.
04
Links and application
In the real world
A stone thrown upwards at a speed of 19.6 m/s, without resistance, rises approximately 2 s and reaches a height of 19.6.
Model verification
Compare the prediction with observation, evaluate the units, the order of magnitude and the influence of the factors not taken into account. Disparity does not always mean an error of law: often idealization is no longer sufficient.
C
What needs to be understood
Outcome 1
Explain the physical meaning of the theme "Free fall" through the model, not just the formula.
Outcome 2
Clear and correctly use terms: free fall, acceleration g, vertical throw.
Outcome 3
Indicate the conditions for the applicability of the law, verify units and limit cases.
T
Terms of the topic
The definition should indicate the physical meaning, not a substitute for a domestic synonym.
free fall
The movement of the body is only subject to gravity in the accepted model.
acceleration g
The acceleration of gravity field gravity at this point.
vertical throw
The movement of the body at an initial speed along the vertical under the influence of gravity in the accepted model.
Air resistance
A force on the air that depends on the speed, shape and size of the moving body.
F
Origin and conclusion of the formulas
The fundamental law cannot be "proven" by algebras: for each record, it is stated whether it is a definition, an experimental law, or a model effect.
v
=
v
0
−
g
t
v=v_0-gt
v
=
v
0
​
−
g
t
model effect
Vertical speed.
The following is an indication of the definition, experience or law from which this entry arises and where it is applicable.
a
y
=
−
g
a_y=-g
a
y
​
=
−
g
The axis is directed upwards, so the acceleration of the free fall has a negative projection.
v
y
=
v
0
y
+
a
y
t
v_y=v_{0y}+a_yt
v
y
​
=
v
0
y
​
+
a
y
​
t
Use the law of speed change at constant acceleration.
v
=
v
0
−
g
t
v=v_0-gt
v
=
v
0
​
−
g
t
The a_y=-g setup shows that the vertical speed is reduced by g every second when you rise.
Conditions:
Traffic near the surface of the Earth without air resistance; the axis is directed upwards, g is considered constant.
Monitoring:
The dimensions of both parts shall coincide; the result shall be checked for sign, order and limit case.
h
=
v
0
t
−
g
t
2
2
h=v_0t-\frac{gt^2}{2}
h
=
v
0
​
t
−
2
g
t
2
​
model effect
Height.
The following is an indication of the definition, experience or law from which this entry arises and where it is applicable.
a
y
=
−
g
,
y
0
=
0
a_y=-g,\quad y_0=0
a
y
​
=
−
g
,
y
0
​
=
0
The beginning of the height count is placed at the point of the drop, and the positive direction is chosen up.
y
=
y
0
+
v
0
t
+
a
y
t
2
2
y=y_0+v_0t+\frac{a_yt^2}{2}
y
=
y
0
​
+
v
0
​
t
+
2
a
y
​
t
2
​
For constant acceleration, the formula for the co-ordinates of the equi-acceleration shall be applied.
h
=
v
0
t
−
g
t
2
2
h=v_0t-\frac{gt^2}{2}
h
=
v
0
​
t
−
2
g
t
2
​
After setting up y_0=0 and a_y=-g are given a height relative to the point of throw.
Conditions:
Vertical drop in a homogeneous field of gravity without air resistance; h is counted up from the point of drop.
Monitoring:
The dimensions of both parts shall coincide; the result shall be checked for sign, order and limit case.
!
Model boundaries and typical errors
Error: Forget model condition
You can't move the formula to any situation just because the letters match. The key condition of this topic is that body mass does not affect the acceleration of free fall in the vacuum.
How to Check the Mind
At the upper point of the drop, the velocity is instantaneously zero, but the acceleration remains equal to g. Then check the unit, vector direction and result behaviour at zero or very large parameter.
Σ
Conclusion on the topic
Free fall
Near the surface of the Earth, all bodies without air resistance fall at the same acceleration g. Vertical traffic is a private case of equal acceleration.
The body mass does not affect the acceleration of the free fall in the vacuum.
At the upper point of the drop, the velocity is instantaneously zero, but the acceleration remains equal to g.
Any numerical result shall be accompanied by a unit, a sign and an explanation of its physical meaning.
The content is consistent with the FRP on Physics of the OS/OSS 2025 and the subject matter of the current lines of the PNP: I. M. Peryškin and co-authors (7–9), G. J. Mäkishev and coauthors (10–11), and with the lines "Engineers of the Future" and V. A. Kasyanov. The original texts are not reproduced, the text of the textbooks is not reproduced.