Physics question

Nitro · Post by **Nitro** » Fri Dec 21, 2007 12:57 pm

Hey ... can some one explain me this ...
I'm going to high school (first grade) so I'm pretty newb.
The acceleration of free fall is 9.8 meter per second^
How is it possible that item what was dropped from some distance
down, without starting speed ( 0 m/s^) in first second felt down by 5 meters?

I know the formula for free fall is
Distance = 1/2 * 9.8 (acceleration of free fall) * time ^

But if we ignore the formula .... the acceleration is 10 m/s^
and the item felt 5 meters in first second ...

Doesnt make any sense ... can some one explain this to me?

[SD]Frites · Post by **[SD]Frites** » Fri Dec 21, 2007 12:59 pm

I think it has something to do with air resistance

Nitro · Post by **Nitro** » Fri Dec 21, 2007 1:01 pm

[SD]Frites wrote:I think it has something to do with air resistance

That was question in test ... it didnt make any sense to me when I followed
the formula ... btw we ignore the air resistance

Dark Shifty · Post by **Dark Shifty** » Fri Dec 21, 2007 1:06 pm

you have to use that 1/2. i remember from my physics class that in 1 second no matter what the object is(with no air resistance) an object falls 4.9 meters. that is half of 9.8 meters per second a second(m/s*s).

so object a falls for 1 second. how far did it fall?

so D= 1/2 * 9.8(acceleration)*1^2(time)

1/2 * 9.8 = 4.9

does that make sense?

Nitro · Post by **Nitro** » Fri Dec 21, 2007 1:08 pm

Dark Shifty wrote:you have to use that 1/2. i remember from my physics class that in 1 second no matter what the object is(with no air resistance) an object falls 4.9 meters. that is half of 9.8 meters per second a second(m/s*s).

so object a falls for 1 second. how far did it fall?

so D= 1/2 * 9.8(acceleration)*1^2(time)

1/2 * 9.8 = 4.9

does that make sense?

Yeah I know ... you just followed the formula ... but I cant get it in my
head that if something had acceleration 10m/s that it done 5 meters in
first second .... I cant understand that ...

Maybe it will get cleaner in my head if I test it ...
I should drop something ^^

Dark Shifty · Post by **Dark Shifty** » Fri Dec 21, 2007 1:10 pm

Nitrozz wrote:
Dark Shifty wrote:you have to use that 1/2. i remember from my physics class that in 1 second no matter what the object is(with no air resistance) an object falls 4.9 meters. that is half of 9.8 meters per second a second(m/s*s).

so object a falls for 1 second. how far did it fall?

so D= 1/2 * 9.8(acceleration)*1^2(time)

1/2 * 9.8 = 4.9

does that make sense?

Yeah I know ... you just followed the formula ... but I cant get it in my
head that if something had acceleration 10m/s that it done 5 meters in
first second .... I cant understand that ...

10m/s is velocity. 10/m/s/s is acceleration. very big difference. just follow the formula and you should be alright. try it again but time at 2 seconds. what does that equal?

Nitro · Post by **Nitro** » Fri Dec 21, 2007 1:18 pm

Dark Shifty wrote:
Nitrozz wrote:
Dark Shifty wrote:you have to use that 1/2. i remember from my physics class that in 1 second no matter what the object is(with no air resistance) an object falls 4.9 meters. that is half of 9.8 meters per second a second(m/s*s).

so object a falls for 1 second. how far did it fall?

so D= 1/2 * 9.8(acceleration)*1^2(time)

1/2 * 9.8 = 4.9

does that make sense?

Yeah I know ... you just followed the formula ... but I cant get it in my
head that if something had acceleration 10m/s that it done 5 meters in
first second .... I cant understand that ...

10m/s is velocity. 10/m/s/s is acceleration. very big difference. just follow the formula and you should be alright. try it again but time at 2 seconds. what does that equal?

Too much for me xD .... And for 2 second is ...
D= 1/2* 9.8 * 2^2
D= 4.9* 4 = 19.6 (near 20 meters)

Hm.... I cant go the find the logic way for free fall ... Guess I'll be sticking to formula .... Physics sux ....

Dark Shifty · Post by **Dark Shifty** » Fri Dec 21, 2007 1:19 pm

Nitrozz wrote:
Dark Shifty wrote:
Nitrozz wrote:
Dark Shifty wrote:you have to use that 1/2. i remember from my physics class that in 1 second no matter what the object is(with no air resistance) an object falls 4.9 meters. that is half of 9.8 meters per second a second(m/s*s).

so object a falls for 1 second. how far did it fall?

so D= 1/2 * 9.8(acceleration)*1^2(time)

1/2 * 9.8 = 4.9

does that make sense?

Yeah I know ... you just followed the formula ... but I cant get it in my
head that if something had acceleration 10m/s that it done 5 meters in
first second .... I cant understand that ...

10m/s is velocity. 10/m/s/s is acceleration. very big difference. just follow the formula and you should be alright. try it again but time at 2 seconds. what does that equal?

Too much for me xD ....
And for 2 second is ...
D= 1/2* 9.8 * 2^2
D= 4.9* 4 = 19.6 (near 20 meters)

Hm.... I cant go the find the logic way for this ... Guess I'll be sticking to
formula ....

you got the question right and it doesn't matter if you don't get it or not. as long as you have the formula, you should be alright

Nitro · Post by **Nitro** » Fri Dec 21, 2007 1:22 pm

Dark Shifty wrote:
Nitrozz wrote:
Dark Shifty wrote:
Nitrozz wrote:
Dark Shifty wrote:you have to use that 1/2. i remember from my physics class that in 1 second no matter what the object is(with no air resistance) an object falls 4.9 meters. that is half of 9.8 meters per second a second(m/s*s).

so object a falls for 1 second. how far did it fall?

so D= 1/2 * 9.8(acceleration)*1^2(time)

1/2 * 9.8 = 4.9

does that make sense?

Yeah I know ... you just followed the formula ... but I cant get it in my
head that if something had acceleration 10m/s that it done 5 meters in
first second .... I cant understand that ...

10m/s is velocity. 10/m/s/s is acceleration. very big difference. just follow the formula and you should be alright. try it again but time at 2 seconds. what does that equal?

Too much for me xD ....
And for 2 second is ...
D= 1/2* 9.8 * 2^2
D= 4.9* 4 = 19.6 (near 20 meters)

Hm.... I cant go the find the logic way for this ... Guess I'll be sticking to
formula ....

you got the question right and it doesn't matter if you don't get it or not. as long as you have the formula, you should be alright

Hehehe ... but I wanted to find some sense in it ... but as you said ...
Follow the formula ... anyway ... Thanks Shifty

Dark Shifty · Post by **Dark Shifty** » Fri Dec 21, 2007 1:28 pm

Nitrozz wrote:
Dark Shifty wrote:
Nitrozz wrote:
Dark Shifty wrote:
Nitrozz wrote:
Dark Shifty wrote:you have to use that 1/2. i remember from my physics class that in 1 second no matter what the object is(with no air resistance) an object falls 4.9 meters. that is half of 9.8 meters per second a second(m/s*s).

so object a falls for 1 second. how far did it fall?

so D= 1/2 * 9.8(acceleration)*1^2(time)

1/2 * 9.8 = 4.9

does that make sense?

Yeah I know ... you just followed the formula ... but I cant get it in my
head that if something had acceleration 10m/s that it done 5 meters in
first second .... I cant understand that ...

10m/s is velocity. 10/m/s/s is acceleration. very big difference. just follow the formula and you should be alright. try it again but time at 2 seconds. what does that equal?

Too much for me xD ....
And for 2 second is ...
D= 1/2* 9.8 * 2^2
D= 4.9* 4 = 19.6 (near 20 meters)

Hm.... I cant go the find the logic way for this ... Guess I'll be sticking to
formula ....

you got the question right and it doesn't matter if you don't get it or not. as long as you have the formula, you should be alright

Hehehe ... but I wanted to find some sense in it ... but as you said ...
Follow the formula ... anyway ... Thanks Shifty

np happy to help

NuclearSilo · Post by **NuclearSilo** » Fri Dec 21, 2007 2:18 pm

formula cant be wrong, only your head is wrong

Nitro · Post by **Nitro** » Fri Dec 21, 2007 2:25 pm

NuclearSilo wrote:formula cant be wrong, only your head is wrong

You got any logical explanation for that Nuclear?

TOloseGT · Post by **TOloseGT** » Fri Dec 21, 2007 2:58 pm

alright, so you know the acceleration is 9.8 m/s^2. that doesn't mean that @ zero seconds, the object's velocity will be 9.8 m/s. objects will always start from zero velocity, and under gravitational acceleration (9.8 ), fall faster and faster until terminal velocity.

EDIT:

at 1 sec, the velocity will be 9.8 m/s, but the object would have had to go through 0 m/s through 9.7 m/s, and during that interval of 1 sec to get there, the object would have fallen only 4.9 m.

Isis · Post by **Isis** » Fri Dec 21, 2007 3:22 pm

OMG this confuses the hell out of me

Sylhana · Post by **Sylhana** » Fri Dec 21, 2007 3:40 pm

Hershey wrote:I hate physics.... I just had my ap physics final this wedsnday....

And ya juss follow the formula and don't ask questions...lol

If it were a chemistry question, I coulda explained to you in great detail <3 lol

Sylhana knows <3

You're such a nerd :love:

schooled me with your chemistry blabla

Bastet wrote:OMG this confuses the hell out of me

+1.

@Nitrozz the easiest way is probably for you to measure up 5metres, time it and drop something. Air resistance increases with speed, as the object moves faster, it collides with more air particles. So initially it will accelerate the fastest, then reach terminal velocity as air resistance balances gravitational pull.

Nitro · Post by **Nitro** » Fri Dec 21, 2007 3:58 pm

TOloseGT wrote:alright, so you know the acceleration is 9.8 m/s^2. that doesn't mean that @ zero seconds, the object's velocity will be 9.8 m/s. objects will always start from zero velocity, and under gravitational acceleration (9.8 ), fall faster and faster until terminal velocity.

EDIT:

at 1 sec, the velocity will be 9.8 m/s, but the object would have had to go through 0 m/s through 9.7 m/s, and during that interval of 1 sec to get there, the object would have fallen only 4.9 m.

That made some stuffs clearer , thanks TOloseGT

phulshof · Post by **phulshof** » Fri Dec 21, 2007 4:01 pm

Starting speed is 0 m/s.
Speed after 1 second is 9.8 m/s.
Average speed during first second is (9.8+0)/2 = 4.9 m/s.
Distance travelled during the first second is 4.9 m.