If you jump out of an airplane, how fast would you fall? What’s the greatest speed you would reach? Let’s practice figuring it out without jumping out of a plane.
This experiment will help you get the concept of velocity by allowing you to measure the rate of fall of several objects. It’s also a great experiment to record in your science journal.
First, you’ll need to find your materials:
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Yes in this section there are more! Also in Unit 2… enjoy!
This was so cool do you have any other projects like this one?
Oh – got it. That’s a really interesting thought you had there. The thing that keeps that from happening is that the shift from atmosphere to space is gradual and not a hard line.
There are special places in orbit that scientists use that keep the forces in balance and it makes the power needed to keep a satellite in orbit minimal due to the gravitational pull of the Earth, moon and sun. You can read about them here: https://en.wikipedia.org/wiki/Lagrangian_point
Keep up the great work and think up new great ideas!
I just thought that the vacuum of space and the atmosphere might both pull on the spaceship and it would eventually split it in half. Grant
No – how did you come to think of that?
Terminal velocity refers to how fast objects move in freefall motion. If you fire a gun from the top of a building to the ground, the speed of the bullet is greater than if you just dropped the bullet. (I’m not suggesting you try this at home – shooting guns from the tops of buildings is never a good idea). I hope this makes sense!
If it were possible to place an object between earth`s atmosphere and space would it be split in half? Grant (10)
If something exploded would some pieces have a higher terminal velocity than others? Grant (10)
I LOVE THAT!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Yes, a lot of them are in Units 1, 2, and also 4 and 5. 🙂 Are you keeping a science journal? If you like recording data, you’ll find one of those very useful!
I like experiments that include dropping things and recording the data. Any others?
Zach
Two things come to mind: first, objects fall at the same rate, not the same speed. There’s no “one speed” for terminal velocity like there is for the speed of light. Terminal velocity is the speed of an object when you add the drag force (which is going to vary with every object) equals the downward force of gravity.
For a skydiver in a freefall position (face town toward the earth) is about 122 mph, but he doesn’t reach that right away. After only 3 seconds of falling, he’s at 61 mph, but it takes 8 seconds to reach 109 mph, and 15 seconds to get to 119 mph… he slowly creeps up on the value.
If he changes his position to be head or feet first, now he’s much more aerodynamic and the projected area is decreased, so he’ll go much faster like the jumper you’re talking about. He also went very high, so he increased the time he needed to reach his desired speed.
The math equation for terminal velocity is: √[(2mg)/(ρACd)]
m = mass
g = acceleration due to gravity = 9.81 m/s2 = 32.2 ft/s2
Cd = drag coefficient (which is different for every object, and determined experimentally)
ρ = density of the fluid (air in this case)
A = projected area of the object (this is where it matters if he’s feet first or face-down)
Secondly, his speed has not yet been confirmed as breaking the sound barrier… but he did reach a very, very fast speed!
i have a question. If in a vacuum all objects fall at the same rate once they reach terminal velocity regardless of weight,and that is a universal speed, then why is it that the man who jumped off the balloon from outer space broke the sound barrier?
three cheers for arora!
Thanks, that would explain it. We just moved, and have only found one of our speakers. Apparently the wrong one. Thanks again.
Some of the first videos we ever made were recorded in mono (don’t ask!) so make sure both speakers are turned up!
Hi, for some reason we’re not getting sound on most of the videos in this section. It seems to be a problem only with those hosted by jwplayer (this is the name that pops up at the beginning). The last video in the section, which isn’t on jwplayer, has sound, and videos in the other sections (also not jwplayer) again work fine. But although the jwplayer videos play fine, there is absolutely no sound.
I love it that you’re asking great questions! Here’s the answer:
Because ALL objects in the earth’s atmosphere are subject to air resistance (drag). To get away from this effect, you need to be in space or on an object without an atmosphere (asteroids, certain moons, etc..)
Air resistance is something that you and I are used to, so it’s a stretch to think of it as something to take into account because our ‘common sense’ tells us that it’s just part of everyday life. But when you remove the air resistance, you can see the effects of gravity by itself without drag. If we were born on a planet without air resistance (and we could survive), this would make intuitive sense, but since we’re on a planet with lots of atmosphere, that’s what we know and are used to, so this is a new idea to think about.
Air resistance example: When you stick your hand out the car window at 65 mph, the amount of air resistance you feel depends on which way you angle your palm: facing the wind or facing the ground. When your palm faces the wind, there’s much more force on your hand, right? The area profile that the wind sees is much greater when your palm faces the wind, and so you’ll feel a lot more air resistance.
The kumquat has a much smaller profile than a cow, so the kumquat will hit the ground first. But if you take them both to the moon, you’ll find they hit the ground at the same time.
Does this help?
On the experiment “A Weighty Issue” in the gravity section it is written, “Gravity accelerates both items equally and they hit the ground at the same time. Any two objects will do this, a brick and a Buick, a flower and a fish, a kumquat and a cow!”
So I know the concept that I am missing is probably something very simple but please help me out. If a cow and a kumquat will hit the ground simultaneously, and taking into account what you’re dropping is not a feather or paper bag (something extra light and prone to a lot of air resistance), why didn’t the objects dropped in the experiment ‘Look Out Below’ hit the ground in the same amount of seconds?
Two objects with the same mass but different shapes will have a different amount of drag on them when moving through the air (the profile that the wind sees is different). For example, a wadded up sheet of paper falls with a greater speed one second after you release it than a flat sheet due to air resistance.
A golf ball and a ping pong ball are the same shape but have different amounts of mass, and will reach the ground at the same time.
Gravity pulls equally on all objects, which means that they all accelerate equally. Did you check out the video about the hammer on the moon that the astronauts did? It’s in the gravity section and it’s really cool!
Hi Aurora,
If gravity accelerates all things equally, why did each of the objects dropped take a different amount of time to hit the floor?
So glad you’re are enjoying the course! You’ll find the Fall Syllabus on the main page near the bottom left, or click here: https://www.sciencelearningspace2.com/2009/07/fall-syllabus/
Hi Aurora,
The course is going well in many ways. My oldest son is asking for a course syllabus. Please send it to us.
Thank you
Rob Rothermel
Ummm… do you mean throwing things around, or taking data? Both are in future experiments, by the way.
I LOVE this expirement because I can record the data and pick different objects. Aurora, are there any more expirements like this?
sevy keble