If I toss a ball horizontally at the exact same instant that I drop another one from my other hand, which one reaches the ground first? For this experiment, you need: [am4show have=’p8;p9;p11;p38;p72;p92;’ guest_error=’Guest error message’ user_error=’User error message’ ]
- 2 rulers or paint sticks. Any thing wide and flat
- 2 coins or poker chips
- A sharp eye and ear
- A partner is good for this one too
Download Student Worksheet & Exercises
1. Place one of the rulers flat so that it is diagonal across the edge of a table with half the ruler on the table and half sticking off.
2. Place one coin on the table, just in front of the ruler and just behind the edge of the table. Place the other coin on the ruler on the side where it’s off the table.
3. Put your finger right in the middle of the ruler on the table so that you are holding it in such a way that it can spin a bit under your finger. Now with the other ruler you are going to smack the end of the first ruler so that the first ruler pushes the coin off the desk and the coin that’s resting on the ruler falls to the ground.
4. Now, before you smack the ruler, make a prediction. Will the coin that falls straight down or the coin that is flying forward hit the ground first?
5. Try it. Do the test and look and listen carefully to what happens. It’s almost better to use your ears here than your eyes. Do it a couple of times.
Are you surprised by what you see and/or hear? Most people are. It’s not what you would expect.
The coins hit the ground at the SAME time. Is that odd or what?
Did you read the first sentence at the top of this lab? What do you think will happen?
The balls will hit the ground at the exact SAME time.
Gravity doesn’t care if something is moving horizontally or not. Everything falls toward the center of the Earth at the same rate.
Let me give you a better example: A bullet fired parallel to the ground from a gun and a bullet dropped from the same height at the same time will both hit the ground at the same time. Even though the one fired lands a mile away! It seems incredible, but it’s true.
Gravity doesn’t care what size something is or whether or not it is moving, Gravity treats all things equally and accelerates them the same.
Notice, that I say gravity accelerates all things equally, not gravity pulls on all things equally. Gravity does pull harder on some things than on other things. This is why I weigh more than a dog. I am made of more stuff (I have more atoms) than the average dog, so gravity pulls on me more.
Weight is nothing more than a measure of how much gravity is pulling on you. This is why you can be “weightless” on a scale in space. You are still made of stuff, but there’s a balance of the gravity that is pulling on you and the outward force due to the acceleration since you’re moving in a circle (which you do in order to remain in orbit), so it feels like you have no weight.
The larger a body is, the more gravitational pull or the larger a gravitational field it will have.
The Moon has a fairly small gravitational field (if you weighed 100 pounds on Earth, you’d only be 17 pounds on the Moon), the Earth’s field is fairly large and the Sun has a HUGE gravitational field (if you weighed 100 pounds on Earth, you’d weigh 2,500 pounds on the sun!).
As a matter of fact, both the dog and I both have gravitational fields! Since we are both bodies of mass we have a gravitational field which will pull things towards us. All bodies have a gravitational field. However, my mass is sooooo small that the gravitational field I have is miniscule. Something has to be very massive before it has a gravitational field that noticeably attracts another body.
So what’s the measurement for how much stuff you’re made of? Mass. Mass is basically a weightless measure of how much matter makes you, you. A hamster is made of a fairly small amount of stuff so she has a small mass. I am made of more stuff, so my mass is greater than the hamster’s. Your house is made of even more stuff so its mass is greater still.
So, here’s a question. If you are “weightless” in space, do you still have mass? Yes, the amount of stuff you’re made of is the same on Earth as it is in your space ship. Mass does not change but since weight is a measure for how much gravity is pulling on you, weight will change.
Did you notice that I put weightless in quotation marks? Wonder why?
Weightlessness is a myth! Believe it or not, one is never weightless. A person can be pretty close to weightless in very deep space but the astronauts in a space ship actually do have a bit of weight.
Think about it for a second. If a space ship is orbiting the Earth what is it doing? It’s constantly falling! If it wasn’t moving forward at 10’s of thousands of miles an hour it would hit the Earth. It’s moving fast enough to fall around the curvature of the Earth as it falls but, indeed, it’s falling as the Earth’s gravity is pulling it to us.
Otherwise the ship would float out to space. So what is the astronaut doing? She’s falling too! The astronaut and the space ship are both falling to the Earth at the same rate of speed and so the astronaut feels weightless in space. If you were in an elevator and the cable snapped, you and the elevator would fall to the Earth at the same rate of speed. You’d feel weightless! (Don’t try this at home!)
Exercises
- True or false? Gravity pulls on all things equally.
- True or false? Gravity accelerates all things equally.
- In your own words, why do the coins hit the ground at the same time? Is this what you’d expect to happen on Mars?
The rest of this experiment is for advanced students…[/am4show]
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For advanced students:
Either now, or at some point in the future you may ask yourself this question, “How can gravity pull harder (put more force on some things, like bowling balls) and yet accelerate all things equally?” When we get into Newton’s laws in a few lessons you’ll realize that doesn’t make any sense at all. More force equals more acceleration is basically Newton’s Second law.
Well, I don’t want to take too much time here since this is a little deeper then we need to go but I do feel some explanation is in order to avoid future confusion. The explanation for this is inertia. When we get to Newton’s First law we will discuss inertia. Inertia is basically how much force is needed to get something to move or stop moving.
Now, lets get back to gravity and acceleration. Let’s take a look at a bowling ball and a golf ball. Gravity puts more force on the bowling ball than on the golf ball. Soooo the bowling ball should accelerate faster since there’s more force on it. However, the bowling ball is heavier soooo it is harder to get it moving. Vice versa, the golf ball has less force pulling on it but it’s easier to get moving. Do you see it? The force and inertia thing equal out so that all things accelerate due to gravity at the same rate of speed!
Gravity had to be one of the first scientific discoveries. Whoever the first guy was to drop a rock on his foot, probably realized that things fall down! However, even though we have known about gravity for many many years, it still remains one of the most elusive mysteries of science. At this point, nobody knows what makes things move towards a body of mass.
Why did the rock drop towards the Earth and on that guy’s foot? We still don’t know. We know that it does, but we don’t know what causes a gravitational attraction between objects. Gravity is also a very weak force. Compared to magnetic forces and electrostatic forces, the gravitational force is extremely weak. How come? No one knows. A large amount of amazing brain power is being used to discover these mysteries of gravity. Maybe it will be you who figures this out!
Advanced students: Download your Forever Falling Lab here.
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It’s not the weight but the SHAPE that determines how things fall through our atmosphere. Try a golf ball and a ping pong ball – they are about the same shape but different weight. Now try a wadded up piece of paper and a straight sheet of paper – these are the same weight but different size. What did you find?
They hit the surface at the same time or nearly hit the ground at the same time, even heavier objects kept falling at the exact same time. What explains this?
The advanced Lab is now part of the HS Physics section that you can access through here: https://www.sciencelearningspace2.com/grade-levels/high-school/advanced-physics/ The lab you are referring to is covered in the first section and includes step by step video instructions.
What are we supposed to put in the worksheet chart? There are no clear instructions.
That sounds fun!
I would try something heavier than a nerf ball, since they’re so light and can be affected easily by air currents. I use a golf ball when doing this, but note that it’s pretty hard to toss one and let go of the other at exact same time, so it will take practice! I wonder if you can design an experiment that will do that… (hint hint!)
Hi Aurora, we tested the forever falling experiment using a foam bullet fired from a NERF gun and the same bullet dropped from an equal height straight down. The bullet dropped from our hand landed first every time. Why??
That’s because the Earth is round, and the center of gravity is at the center of the Earth, inside the ball (Earth) at the core. This means that if you’re at the south pole, it still feels right-side up because gravity is pointing down toward the center of the Earth, same as it does for the North pole and on the equator. If the direction of the gravitational field was indicated by an arrow that pointed from north to south pole, then people on the south pole would feel upside-down. But instead, that arrow points from the surface of the planet to the core at the center. Does that help?
Hi, I know that gravity keeps me from falling off Earth. I would like to know why I don’t feel like I’m sideways in North America where I live, and penguins are not upside down in Antartica. Thank you.
Good question! The answer is sadly, no – you need to be about the size of a planet to have any effect of “pulling things toward you” – at least, enough for it to be noticeable.
Hi Aurora! We were doing the gravity unit, and I was wondering, we have our own gravitational fields, but they are so small compared to the earth’s that it doesn’t do anything. But what if we were way out in space? Would we be able to pull things towards us?
Thanks,
Ally W.
Nice work varying the experiment!
And great question! Did you watch the Feather and the Hammer video yet? It answers that exact question. It’s the second video on the page (link above).
Dear Aurora,
We tried the experiment with different sized coins and some odd-shaped objects (such as dog toys). We had a hard time doing it with the paint stick diagonally, so we just put the objects at the edge of the table and shoved them off using the paint stick, and got the same results that way. My son, Asher, had a question: What if one object was in an airless space when it was dropped?
Thanks!
Benita
Great question! Think of the path they travel through as having two different components: the vertical drop and the horizontal distance.
The vertical drop: The coin and ruler are both in a sea of air (the atmosphere) and since they are not the same shape, they are going to have to push aside different amounts of air as they fall to the ground (air resistance). If we take away this air (like visiting the moon), you’ll be able to see them both hit the ground at the same time.There’s a video in this section that shows a hammer and a feather hitting the ground at the same time – make sure you watch it… it’s super-cool.
The horizontal distance: Both objects are still affected by air resistance. The larger object will experience more drag and not travel as far as a streamlined object. How far each goes also depends on the vertical drop: the less air resistance, the more time it has aloft, and the further it will go.
The direct response to your question is that gravity accelerates all things equally: things fall at the rate of 9.81 m/sec2 or 32.2 ft/s2
Does that help?
hi,
This experiment is mind boggling to us.We have attempted to do the ruler and coin experiment. We filmed it on a HD camera and we have found that the coin which is hit with the ruler seems to takes longer to get to the ground. Are you saying that the amount of force behind an object being thrown does not influence how quickly it drops?
Ben and Caleb
That is cool! I was a little skeptical at first but I saw the results! Thanks Aurora, you have made science fun again.
It has to do with gravity. Stuff falls at the same rate no matter what it weighs, and when you do the math to figure it out, it comes out to be 16 feet the first second. You can read more about gravity here and do a couple of gravity experiments here especially the super-cool gravity experiment that the astronauts did on the moon!
You said that everything falls sixteen feet within the first second. Why always sixteen feet?
Krishnaya, age 8
Mythbusters did an episode about the bullet experiment. They shot one bullet from a gun while simultaneously dropping another one to test whether they would hit the ground at the same time or not. I found the video on youtube http://www.youtube.com/watch?v=D9wQVIEdKh8
Again, thank you Aurora, my children are now enjoying Unit 1 lesson 2 as much as they enjoyed lesson 1.. if not a bit more 🙂 now that we are used to the format.