Question

hey guys.... when does an object start to get pulled down by the force of gravity, how slow does it have to go? thanks!

Answer 1

It will not slow, it will accelerate, with the g gravity force...

Answer 2

ah wow interesting! so when the object is in the air it accelerates until it hits the ground (until it hits terminal velocity) so my question is, no matter how fast an object is going it will get pulled down no matter what.

Answer 3

Ok, it's a rectilinear movement, so, you position at initial time is, for example: h, your initial velocity is 0(because you let the object fall without impriming any force), and you acceleration is: -g
So your particle movements will be determined by: s(t)=h+0*t-(g/2)*t^2, where s is the movement function respect the time.
From what you've write I think that you would say how much time it have before touche the ground, to do this, simple put s(t)=0=h-(g/2)*t^2 and soooo => t^2=2h/g => t=sqrt(2h/g) and there is your time! ;) (think that i didn't noticed minus sign before square root, it's because your object... just can't go backward in time!!)
Last thing, acceleration grown up if the velocity have the same direction, so in fall, the velocity go down, and the -g too, so your object speed it up! :D

Answer 4

Nothing against decripter, but let me see if I can explain this so that you can understand what is going on!

If we are looking at objects on earths relative surface (basically anything that is within the atmosphere) then that object has earth's gravitational force acting upon it. And for a change in movement (velocity) to occur, a force must first act upon it (Newton's first law). So when you throw a ball, earths gravitational force is causing a change in the balls velocity, and in most cases, this change makes the ball slow down (...this must mean that the force of earth's gravity is opposing the force that you applied initially to the ball....!!!)

So that being said, read what ive written and see if it helps with your current problem! If irrelevant now, it will definitely come in handy later down the road!

F(of earth's gravity)=ma; where "m" is the mass of the object in kg, and "a" is the acceleration of earth's gravity measured in m/s^2, acting on it (which is a constant and, for simplicities sake, is denoted "g" and has a value of 9.8m/s^2).

Normally when dealing with problems concerning the force of earth's gravity F=MA is written F=-mg. This is because (when using the force of earth's gravity at a BASIC level) "a" is a constant (9.8m/s^2), thus can be substituted with "g".

To understand why we include the "-" in the equation, think about it like this:
We usually use a coordinate system for forces on earth where the up direction (away from earth's center) is in the positive "y" plane and anything in the down direction (towards the center of the earth) is in the negative "y" plane. (think of your standard x/y cartesian coordinate system). That being said, MOST forces applied are done away from earth's center, thus in the positive direction, and since the force of earth's gravity is always towards the center of the earth its in the negative direction and so we write "-" in front of it. If you were to throw a ball straight down, you would be applying a negative force to it as well.
NOTE: I said we USUALLY use this coordinate system when dealing with forces on earths surface. Whether you say that the direction away from earth's center is positive or negative is totally arbitrary and up to you, just remember to adjust all your "-"/"+" accordingly!
NOTE: In order to not ramble more than I already have, I have simply been saying that the force as a whole is what is in the negative direction. This is true but if you look at force, "ma", the acceleration is what is really giving it the negative value since "m" is only a quantitative value (scalar to be exact) and doesn't have direction. But since force is directly proportional to "a", we know that when one is negative the other must be as well!

Remember, this is put SIMPLY and should suffice for all beginner level physics courses. If you want to understand it more at depth, let me know and I would be happy to explain it what really is going on!

I know this is extremely long winded, but hopefully this cleared up any questions!

Answer 5

@hyperchemist when the displacement and acceleration will be in same direction then the velocity of particle increases and if in opposite direction then velocity will decrease . in your question, the object will fast not slow....