Gravity and Small Objects

[moca mola]

I just had a thought, and then another one! *ding ding*

anyway, how come small things don't seem to be affected so much by gravity?

eg.. i take a baby green tree frog from my house (around 3cm or less) and take it outside and launch it from my hands onto the grass.

now if that was me being launched from the top of my house or higher i'm sure i'd suffer at least some broken bones, and to the best of my knowledge the frog suffers no damage.

how does that happen?

ps. my 2nd thought was "I know, I'll ask on OCAU!" w00t.

[vec]

I guess you need to put things into perspective.

The same question could be applied to ants. They can carry upwards of a thousand times their own weight, why cant humans do that?

[NanoDuke]

The key here is mass. There is a major difference between a small animal and a human body.

F=m*a
If you have greater mass, then more force is required to result in the same acceleration.

A frog landing from your hand will be going much faster then you will from a rooftop on impact, due to the above relation.
Also, wind resistance can be taken into consideration too.

Also, think about the surface you are landing on. A frog can most likely be supported on the tops of the blades of grass. Whereas we crush grass right to the dirt.
A frog falling into grass is comparable to falling into a foam pit. The foam compresses until the force gravity pulling you down is equalised with the force of the foam pushing you back up. Have too little foam and you'll hit the ground, still breaking something.


There are heaps of other situations to get you thinking about mass and acceleration. Like, for example, why do most buses not have seatbelts?
A bus' mass is >> than a small sedan. If the two collide at an intersection at 90 degrees to each other, the bus will throw the sedan out of it's way. The car will spin violently, maybe even flipping over, while the bus will only slightly loose a bit of momentum. Think of the many collisions in the movie Speed.
The occupants of the sedan will be in a lot of trouble, but passengers on a bus may only slightly lurch forward.
Remember that F=m*a works in "reverse" too. A really heavy object requires a great deal of force to decellerate it.

[moca mola]

haha awesome. you guys make it all sound so simple! i wish i was a frog, or that the world was full of foam pits.

btw, why can ants lift 1000 times their own weight?

[Goth]

Originally Posted by NanoDuke

If you have greater mass, then more force is required to result in the same acceleration.

A frog landing from your hand will be going much faster then you will from a rooftop on impact, due to the above relation.

The acceleration due to gravity on or near the Earth's surface is constant, for any falling object.

If you fall from the same distance as the frog, you'll be travelling at the same speed (almost, ignoring air resistance) when you hit the ground.



But because you have more mass, you'll have more momentum and kinetic energy.

[NanoDuke]

moca_cola, I was getting to that.

Think of what muscle is. It's basically a bundle of fibres which can contract and create a pulling force. Ant's muscles are pretty much the same composition as ours.
*And this will probably help to build up a better picture of a frog landing*

Ant muscles are no stronger than human muscles on a pull-for-pull basis, but the small size of ants gives them an advantage on how much muscle force they can produce.

Oh and it's more closer to 50 times their weight, not 1000 lol.

/Slaps head.
I don't know why I made that mistake about the same velocity of the objects. Sorry Goth

Yep, got it wrapped around my head now. I was just getting confused with what I was thinking of. Greater mass means more stopping power needed, which lead me to the foam analogy.

[moca mola]

Originally Posted by NanoDuke

moca mola, I was getting to that.

Think of what muscle is. It's basically a bundle of fibres which can contract and create a pulling force. Ant's muscles are pretty much the same composition as ours.
*And this will probably help to build up a better picture of a frog landing*

Ant muscles are no stronger than human muscles on a pull-for-pull basis, but the small size of ants gives them an advantage on how much muscle force they can produce.

i'm not sure i understand this time.. if an ants muscles are on a scale similar to our own then why does their size matter? like do u mean if an ant was human size it would be equally as strong as us?

[Deckham]

Originally Posted by moca mola

i'm not sure i understand this time.. if an ants muscles are on a scale similar to our own then why does their size matter? like do u mean if an ant was human size it would be equally as strong as us?

All things being equal, yes. Because they will have greater mass to move, including their own mass.
That's 'mass' in relation to the Earth.

[moca mola]

Originally Posted by Deckham

All things being equal, yes. Because they will have greater mass to move, including their own mass.
That's 'mass' in relation to the Earth.

ah k w00t. mass in relation to Earth, i get it now, though havent entirely got it sorted in my brain. thanks

no more need to fear giant ants destroying the world, i'll grapple those bitches like Jebediah Springfield.

[NanoDuke]

Yep, if ants get bigger the individual fibres won't get any larger. Humans just have more of them bundled together, like a bungee cord.
One single muscle fibre can only exert a certain force. Bodybuilders are strong because when exercising the body creates more fibres which then work together to exert greater force in total.

[spludgey]

I'm surprised no one has said this yet: Terminal velocity is much lower for small objects as (surface area)/mass is much bigger.