The one drawn in black implies that the velocity of the ball will increase forever with distance but this cant be true with normal laws of physics
In blue the speed of the ball levels out when it reaches a terminal velocity (im assuming that it is being thrown from a tall cliff or something similar)
Also blue has a decreasing not increasing gradient
Edit: Im in a rush so this is very brief but if you need further clarification feel free to ask

(edited 3 years ago)

Reply 6

username3477548

Original post by Josh_J

thank you very much for ur response. Makes more sense now, but i thought the gradient would always be increasing as g, 9.81, is always causing the ball to accelerate right?

Original post by summerberry19

Is it a velocity-time graph?

velocity distance graph xx

Original post by Eimmanuel

What do you really mean by a graph of a ball thrown?
Explain why both graphs/curves have an increasing gradient.

a ball being thrown from a cliff or something tall. the gradient would always be increasing as g, 9.81, is always causing the ball to accelerate right? so the velocity is always increasing like an exponential?

(edited 3 years ago)

Reply 7

ran-dumb

Original post by vix.xvi

thank you very much for ur response. Makes more sense now, but i thought the gradient would always be increasing as g, 9.81, is always causing the ball to accelerate right?

velocity distance graph xx

a ball being thrown from a cliff or something tall. the gradient would always be increasing as g, 9.81, is always causing the ball to accelerate right?

I don't do physics so I may be wrong, but isn't acceleration constant, so constant gradient and hence a straight line? There is air resistance or whatever but shouldn't stop the graph from doing that at the start at least

Reply 8

username3477548

sorry the graph is meant to be of a ball being thrown down not up i think x

Original post by *****deadness

its not a straight gradient cuz a gradient on a speed distance graph represents v/s which is metres per second per metre...which cancels to give 1/s ?

Reply 9

ran-dumb

Original post by vix.xvi

sorry the graph is meant to be of a ball being thrown down not up i think x

its not a straight gradient cuz a gradient on a speed distance graph represents v/s which is metres per second per metre...which cancels to give 1/s ?

Oh it's not the usual speed time graph. Then yeah it would be different

Reply 10

Josh_J

Original post by vix.xvi

You would be right to say that the gradient of the graph would always increase assuming that there was no air resistance. Here is the explanation for why it levels off as speed increases and hence does not keep increasing
As speed/ velocity increases air resistance increases
initially the force of gravity downwards is greater than the force of air resistance up wards
so the ball accelerates downwards and hence its speed increases (This is the inital part of the blue graph)
Eventually air resistance upwards will equal the force of gravity downwards .
at this point gravity downwards = air resistance upwards and terminal velocity is reached
this means velocity/speed will stay constant (the final part of the blue graph where its gradient is decreasing. If you continued to draw it it will form a straight line)

Where I think you are confused is that you are assuming that there is no air resistance which will meant that the constant force of gravity (9.81) will keep increasing the speed as acceleration is the rate of change of speed. Even though acceleration is constant (remember gravity is always constant) it will keep having an affect on speed and thus increasing it for example if I had an inital speed of 2m/s and my acceleration is 2m/s^2 it will keep increasing like this. 2,4,6,8... so on and will never stop. This is your misconception. It will eventually start decrease when air resistance is present so... 8, 10, 11, 11.5, 11.55,11.56... until a constant value is reached as gravity is not the only force present - Refer to the explanation above
PS: i havent studied physics since GCSE so may be rusty with the terminology but Im pretty sure the concept is correct

Reply 11

username3477548

Original post by Josh_J

PRSOM

aww thank so much!! that makes wayyy more sense. rly appreciate ur time.. :smile:

Juts one quick question, so if air resistance wasn't a thing, would the graph be like the one I've drawn in balck? :smile:

Reply 12

flaurie

Volunteer Team

Original post by vix.xvi

Juts one quick question, so if air resistance wasn't a thing, would the graph be like the one I've drawn in balck? :smile:

Gravity might have something to say in it :wink:

Reply 13

Josh_J

Original post by vix.xvi

PRSOM

aww thank so much!! that makes wayyy more sense. rly appreciate ur time.. :smile:

Juts one quick question, so if air resistance wasn't a thing, would the graph be like the one I've drawn in balck? :smile:

No problem and that would depend on if the object is the object has constant or changing acceleration
so if you remember from my example if you started at 2m/s and had a CONSTANT acceleration of 2m/s^2 then your speed would increase like 2,4,6,8,10.... forever (assuming that no other force is causing resistance.
Therefore for CONSTANT acceleration it would be a directly proportional straight line through the origin
however if acceleration is CHANGING then it would indeed look like the line in black.
say if again we started at 2 m/s and there was an acceleration present of 2m/s^2 in the first lets say the first 3 seconds of travelling and then if that acceleration changed to 3 m/s^2 in the next 3 seconds then your speed values would look like this 2,4,6 (first 3 seconds), 9,12,15 (the next 3 seconds)
if you were to graph that then it would look like one line joined to another with the second line being at a higher gradient so it slopes up essentially (like the black line in your picture). Since with these things acceleration changes more rapidly then I have stated for the sake of this example it will slope up but look like a smoother curve. Id reccomend searching on google speed time graph for constant acceleration and then speed time graph for changing acceleration.
Hope this helps and btw if you are studying this for GCSE im about 70% sure that they wont ask you anything too complicated when it comes to changing acceleration and velocity time - graphs as we cover this at A level. Although please check it your specification for your subject yourself to be sure. And oh yeah almost forgot. For the sake of the ball falling from a cliff or something like that assuming it never reaches the ground (and ignoring air resistance) since acceleration is constant (which it is as it is 9.8 m/s^2 for gravity) then it will look like a directly proportional line graph that increases to infinity.