When two different stones weighing was dropped without initial velocity of
the same height in the same time, the stone Which till the ground
first ?
The events referred to above in Physics as a free fall, which is a straight motion
uniformly on a vertical trajectory. His trademark is a falling object without
initial velocity (vo = zero). The more downward motion of objects more quickly.
Figure 3.1: Two stones are dropped from the same height and in
time
Acceleration experienced by each object in free fall is always the same, ie same
with the acceleration of gravity (acceleration of gravity on earth would you
learned in the module to 3).
In this module, you simply know that the earth's gravitational acceleration magnitude
 |
| Figure 3.2. The object experiencing free fall acceleration equal to the acceleration of gravity. |
accelerated that we discussed in
previous activities remain valid, only
Just get rid of our vo from equation
because the price is zero and the symbol s in
these equations we replace
by stating the height h and
we replace a with g.
Thus, it is now the third equation:
Notice the similarity of the second free fall.
When the left and right sides equally we multiply by 2, we get:
or
so,
The equation of free fall time of falling objects
equation of time.
From the equation of time to fall, it appears that when the object falls freely only
influenced by two factors: h = height and g = acceleration of gravity.
So the weight of other quantities do not affect the fall time.
This means that although different weight, the two objects falling from heights
together in the same place will fall at the same time.
In our daily life might be another occurrence. Different bodies
weight, would fall in the not concurrent. This can happen
due to air friction. Experiments in the vacuum tube
prove that a feather and a coin fall within the fruit
same time.
example :
1 . A high jumper leaps into the air with an initial speed of 5.8 m/s. how high will she be at the top of her flight, when v = 0 ?
solution
if we choose the ground level as the origin of our y - coordinate axis and the y axis points up, then the know quantities for this problem are :
yo = 0
vo = 5.8 m/s
a = -g = - 9.8 m/s²
we wish to know the value of y when v = 0. so we can use the formula :
y - yo = v² - vo²/ 2a = 0² - ( 5.8 m/s )²/2(- 9.8 m/s²)
= 1 .7 m
2 . From one part of the building height of 20 m, two pieces of stone is dropped
sequentially. The mass of the two stones each 1 / 2 kg and 5 kg. when
acceleration of gravity at that place g = 10 m/s², find time to fall to
The second stone (Ignore air friction)
solution :
Because of air friction is negligible (usually rightly so), then the motion
The second rock fall time satisfies the equation of motion in free fall.
For the first stone,
h1 = h2 = 20 m,
m1 = 0.5 kg
m2 = 5 kg
g = 10 m/s²
t1 = ? and t2 = ?
= √4
= 2 second
For the second stone,
h1 = h2 = 20m, so that t2 = t1 = 2 seconds
Thus, objects that fall free of the same height in a
equal (= acceleration of gravity equal) will fall in the same time.
-Laboratory activities
You try to do experiments with your friends. Look for a place in
environment where you can knock them freely. more and more
high spot of ground, the better, such as a tower. order
Your friends waiting at the bottom of the tower. While you are on top of the tower.
Once your friend is ready, throw an object (eg ball) down
the tower. Have your friend record the time of falling objects by using
stopwatch or digital watch.
3. A monkey dropped the durian fruit from the tree (g = 10). Of altitude when the fruit was dropped in 1.5 s the fruit reach the ground? What is the speed of the durian, 1 s since dropped?
Figure 3.5: The fruit durian experience free fall.
previous activities remain valid, only
Just get rid of our vo from equation
because the price is zero and the symbol s in
these equations we replace
by stating the height h and
we replace a with g.
Thus, it is now the third equation:
 |
| Equations of free fall Description: g = acceleration of gravity ( m/s²) h = height of object (m) t = time (s) vt = velocity at time t (m / s) |
Notice the similarity of the second free fall.
When the left and right sides equally we multiply by 2, we get:
or
so,
The equation of free fall time of falling objects
equation of time.
From the equation of time to fall, it appears that when the object falls freely only
influenced by two factors: h = height and g = acceleration of gravity.
So the weight of other quantities do not affect the fall time.
This means that although different weight, the two objects falling from heights
together in the same place will fall at the same time.
In our daily life might be another occurrence. Different bodies
weight, would fall in the not concurrent. This can happen
due to air friction. Experiments in the vacuum tube
prove that a feather and a coin fall within the fruit
same time.
 |
| Figure 3.3: Chicken Feather and coin in vacuum tubes. |
1 . A high jumper leaps into the air with an initial speed of 5.8 m/s. how high will she be at the top of her flight, when v = 0 ?
solution
if we choose the ground level as the origin of our y - coordinate axis and the y axis points up, then the know quantities for this problem are :
yo = 0
vo = 5.8 m/s
a = -g = - 9.8 m/s²
we wish to know the value of y when v = 0. so we can use the formula :
y - yo = v² - vo²/ 2a = 0² - ( 5.8 m/s )²/2(- 9.8 m/s²)
= 1 .7 m
2 . From one part of the building height of 20 m, two pieces of stone is dropped
sequentially. The mass of the two stones each 1 / 2 kg and 5 kg. when
acceleration of gravity at that place g = 10 m/s², find time to fall to
The second stone (Ignore air friction)
solution :
Because of air friction is negligible (usually rightly so), then the motion
The second rock fall time satisfies the equation of motion in free fall.
For the first stone,
h1 = h2 = 20 m,
m1 = 0.5 kg
m2 = 5 kg
g = 10 m/s²
t1 = ? and t2 = ?
= √4
= 2 second
For the second stone,
h1 = h2 = 20m, so that t2 = t1 = 2 seconds
Thus, objects that fall free of the same height in a
equal (= acceleration of gravity equal) will fall in the same time.
-Laboratory activities
You try to do experiments with your friends. Look for a place in
environment where you can knock them freely. more and more
high spot of ground, the better, such as a tower. order
Your friends waiting at the bottom of the tower. While you are on top of the tower.
Once your friend is ready, throw an object (eg ball) down
the tower. Have your friend record the time of falling objects by using
stopwatch or digital watch.
 |
| Figure 3.4: Comparing the fall time various objects Do it repeatedly and for different different bodies. Compare the fall time range of the object. Is it different? When you do this experiment carefully, You select objects that are solid and round (not the board, let alone the paper), you will get that time it will all fall together. |
3. A monkey dropped the durian fruit from the tree (g = 10). Of altitude when the fruit was dropped in 1.5 s the fruit reach the ground? What is the speed of the durian, 1 s since dropped?
Figure 3.5: The fruit durian experience free fall.
Completion: We use the second equation to calculate the height of free fall. So,
= 1/2 . 10 (1,5)²
= 5 (2,25)
= 11,25 meter
We use the first equation to calculate the speed. So,
vt = g.t
= 10. a
= 10 m / s
What is the velocity of an object during free fall from a height of 5 m
right when arriving at the ground (assuming g = 10)?
completion:
We use the third equation in free fall.
vt² = 2.g.h
= 2. 10. 5
= 100vt = 10 m / s
Sources :
Phisics a general introduction / second edition
ALAN VAN HEUVELEN
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