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F=ma ?? what if "a" is zero?
Obviously, I'm missing something quite basic. However, if a 1,000 kg object is traveling 200 kilometers per hour......but NOT accelerating, what force would it exert when it hit you?
By formula: the Force would equal 1,000 kilograms times zero. Thus....ZERO.
What am i missing?
Three good answers so far. But still, it seems a bit fuzzy. Perhaps the definition of "force" is the problem (not formula)?
In the F=ma equation, a bat striking a baseball is always use. It's said that the force on the baseball, from the acceleration of the bat and its mass is what causes the baseball to reverse direction, and how fast and how far.
It still seems odd, and I'm at a bit of a loss to understand how a 1,000kg object traveling at 200 k/h......but not accelerating, has no force. Torque? yes. Energy? yes. Capable of doing work (torque)? yes. But.....zero force??
If I swung a baseball bat at a constant speed (and assuming the ball doesn't compress/rebound and the bat doesn't flex at all).....the ball should not even slow down. It should continue through the bat....since force is zero.
I surly am missing something super-basic. ?? Can someone explain to me what it means when FORCE is zero....yet kinetic energy is massive?
Edit 2- Or...perhaps I'm mixing up my parties (force and acceleration). Perhaps the acceleration is the RESULT of the bat hitting the ball (even if the bat is not accelerating). So....the acceleration is still there, it's just all in the ball. Thus, the force would be calculated algebraically, based on the mass of the BALL (or car) and the acceleration of the BALL (or car).
?
3 Answers
- twopairacesLv 47 years ago
To start, if the velocity of the 1000kg object as it travels through space is constant, and its acceleration is zero, the forces at work upon the object sum to zero.
However, when it HITS you, two things start happening:
1) The object stops moving at a constant velocity.
2) You start moving at some velocity.
In short, the acceleration of, and therefore the forces at work upon, the object (and you) is no longer zero.
......
Concerning your bat and ball example:
You have made an improper assumption about the bat -- it is impossible for it to NOT be subject to an acceleration. There will be a force pair: the bat will exert a force on the ball, causing an acceleration on the ball, and the ball will exert a force on the bat, causing an acceleration on the bat.
I suggest this video:
- ?Lv 77 years ago
1,000 kilogram object = Weight
Weight = Mass * Gravity
Gravity = acceleration
Weight = Force
Travelling at a constant speed means acceleration is constant.
V(t) = 200 t
V ' (t) = A(t) = 200 = constant acceleration
Being hit with a 1,000 kg object travelling 200 km / hour tells us the Work and the Momentum.
- Anonymous7 years ago
It has momentum in the static state (no acceleration). In your example when your object hit you it would then have acceleration (negative) based on your mass when it hit you.
