Basic kinematic physics equations do not make sense to me.

In summary, the SUVAT equations can accurately predict the distance an object will fall in a given amount of time, as long as air resistance is not a factor. The equation ΔX = ViT + 1/2AT^2 can be used to calculate the distance an object will fall in 2 seconds, which in this case is 19.6 meters. Despite initial doubts, these equations have been tested and proven to be accurate reflections of reality.
  • #1
zeromodz
246
0
If I drop a ball, how far will it fall in 2 seconds?
ΔX = ViT + 1/2AT^2
ΔX = (0)(2) + 1/2(9.8)(2)^2
ΔX = 19.6 m

I tested this, and there is no way an object falls 19.6 m in only 2 seconds. Think about it. Drop something right now and it will only fall like 1 meter in one second. I don't understand. These equations don't fit reality to me. Can someone show me what I am doing wrong?
 
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  • #2
Yea make your test more accurate.
 
  • #3
The equations are fine.
One answer is misperception. When the object lands it takes the brain at least 200ms before you register that the object hit the ground. And some more time before you hit the stop watch again.
 
  • #4
Don't "think about it", just go up 20 meters and drop something. See how long it takes, then come back with the results.

You have to be willing to set aside what you "think" and be open to other possibilities.
 
  • #5
SUVAT equations don't take into account air resistance, so strictly an object will take 2 seconds to fall that distance in a vacuum.

Also, given that the object accelerates at 9.8ms-2, after one second of falling it will have a velocity of 9.8ms-1, so it will be traveling quite quickly after two seconds and hence of covered quite a distance. I believe it makes more sense if you consider it that way.
 
  • #6
What is a SUVAT equation?
 
  • #7
I certainly wouldn't want to free fall for 2 seconds. That's like a fall from a 5 story building...splat. 2 seconds is longer than you think. Try throwing a ball straight up in the air as high as you can and count how long it takes to fall back down.
 
  • #8
Phyisab**** said:
What is a SUVAT equation?

SUVAT equations are equations like you mentioned at the beginning of the thread, such as
s = ut + 1/2at^2 , or v = u + at. They are named SUVAT equations because they all contain either the terms s, u, v, a or t.
 
  • #9
The equations are straight forward
and very self explanatory, i don't see
a problem with it...
 
  • #10
There is no problem with those equations. They reflect reality on a classical level just fine.

zeromodz said:
If I drop a ball, how far will it fall in 2 seconds?
ΔX = ViT + 1/2AT^2
ΔX = (0)(2) + 1/2(9.8)(2)^2
ΔX = 19.6 m

I tested this, and there is no way an object falls 19.6 m in only 2 seconds. Think about it. Drop something right now and it will only fall like 1 meter in one second. I don't understand. These equations don't fit reality to me. Can someone show me what I am doing wrong?

Trust me an object dropped will travel much farther than a meter in one second. If you really want to test this out, try doing something compared to what Galileo did by having a ball roll down a ramp. You can much more easily time how far the ball has moved because the ball is moving with an acceleration smaller than g. You will find that the times you get will be in perfect harmony with those kinematic equations
 

1. How do I know which kinematic equations to use?

There are four main kinematic equations that are commonly used to solve problems involving motion:
1. v = u + at (equation for finding final velocity)
2. s = ut + 0.5at^2 (equation for finding displacement)
3. v^2 = u^2 + 2as (equation for finding final velocity without time)
4. s = 0.5(u + v)t (equation for finding displacement without acceleration)
To determine which equation to use, you need to identify what information is given in the problem and what you are trying to find. Each equation can be used to solve for a different variable, so choose the one that aligns with the information you have and the variable you are trying to find.

2. What do the variables in the kinematic equations represent?

The variables in kinematic equations represent:
- v = final velocity (m/s)
- u = initial velocity (m/s)
- a = acceleration (m/s^2)
- t = time (s)
- s = displacement (m)
It is important to pay attention to the units of each variable in order to ensure that your calculations are correct.

3. Do I always need to use all four kinematic equations?

No, you do not always need to use all four kinematic equations. In some problems, you may be given enough information to solve for the unknown variable using just one equation. However, in more complex problems, it may be necessary to use multiple equations to find the answer.

4. Can I use kinematic equations for any type of motion?

Yes, kinematic equations can be used for any type of motion as long as the acceleration is constant. This means that the velocity of the object is changing at a constant rate. If the acceleration is not constant, more advanced equations and concepts, such as calculus, may be needed to solve the problem.

5. What should I do if my answer does not make sense?

If your answer does not make sense, double check your calculations and make sure that you have used the correct equation and input the correct values. It is also helpful to compare your answer to the given information and use your knowledge of physics to determine if the answer is reasonable. If you are still unsure, seek help from a teacher or tutor to guide you through the problem-solving process.

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