Physics Question---F=ma?

Question

Take a mass of 100 grams, and gravity's acceleration, 9.81m/s^2.

Let's say you drop the 100g object from a building

If F=ma, does that mean that the 100g object hits the ground with the same force, no matter how high you drop the object from? Because m is always 100g, and gravity is always 9.81m/s^2?

Answer 1

the force would = 100x9.81 = 98.1N

Answer 2

That is correct. The force from the gravity is always the same. However, if you are not high enough to reach terminal velocity, the speed the object is traveling will vary with the height from which it is dropped. But this has no effect on the force.

Answer 3

You're correct in your implied assumption that that conclusion doesn't make sense.

When things accelerate, they speed up. The longer it falls, the faster it gets.

When it hits the ground, it has to stop, and to do this, it decelerates, or has negative acceleration.

That is the acceleration that's important in calculating the force.

Example: a 10kg object is dropped from a certain height, so that at the instant before it hits the ground, it's going  50 m/s.

Same size object, dropped right above the ground is only going 10m/s when it hits. So they'll decelerate at different rates when they hit, changing the A in the equation. I

If two objects are dropped from different heights that are both really high, they'll reach terminal velocity, when they won't accelerate any more, and they'll hit at the same speed, so F will be the same.

Answer 4

Since F=ma, then a=F/m. That may clarify things for you.

Answer 5

You are confused. You are thinking of f=mv. Gravity is 9.81m/s^2. This is an acceleration, not a velocity, which means that the greater the number of seconds, the greater the velocity. In other words, the higher the object is dropped, the greater the amount of time, here s, and so the greater the force.

Answer 6

No. You have input the mass of the object and the acceleration of the object due to gravity. You have not told the equation anything about the ground. What you have found is the force of gravity acting on the object, regardless of the ground. To find the force when it hits the GROUND, you would have to know the acceleration that the GROUND imparts to the object when it hits.

Answer 7

Yes.  I strongly agree.

Answer 8

You're not entirely mistaken. F = ma is correct, but what you were comparing is the weight of the object (where a = g, the acceleration due to gravity), versus the force the object undergoes due to rapid deceleration when it hits the ground.

An object dropped from 2 meters imparts twice the force on impact as one dropped from 1 meter.

Here a link to a handy Web site:

http://hyperphysics.phy-astr.gsu.edu/hba...

Answer 9

it depends on the distance it falls and whether it reaches terminal velocity or not. an object of a 100g falling 10m will have more impact than the same object falling 5m, mainly because it would have an extra 5m to acellerate at 9.8m/s. a 100g object falling from 200m would have the same impact as one dropped from 1000m if it reaches terminal velocity after 199m, seeming it reached a point where it doesn't accellerate any longer. Once it stops accellerating the impact peaks and the force would be the same. but don't take my word for it, i'm using drummer logic...

Answer 10

But every seceond it is accelerating another 9.81 m/s sq. The speed is not constant. The longer it is pulled upon by gravity, the harder and faster it will hit the ground.

Answer 11

You must do some thinking boy. You might jump from a 100m high building, believing height do not matter.

The acceleration is constant 9.81m/s^2.

This tell you that the speed increase 9.81 m/s each second the body is falling.

To know the speed of the body hitting the ground, you need to know ether the height ore the time gone during the fall.

But you must notice that the weight of the body do not influence on the speed or time. The wight only contribute to the moving energy.

v= gt anyhow.

E=mgh= potential energy used by lifting the body up.

Moving energy hitting the ground is equal to potential energy  used by lifting.

Answer 12

F=ma  gives you the weight of the object which does not depend on its height of drop.  The force on impact is given by  the decelleration X mass of the object. This is why you bend your legs when jumping from a wall when you land and cars have crumple zones.  The effect is to prolong the time of decelleration and make the resultant decelleration and force smaller.

Answer 13

if you mean Momentum ( http://en.wikipedia.org/wiki/Momentum )

it depends on velocity and velocity depends on height

p=mv