is the acceleration of an object moving up and down always -9.8m/s^2?

Question

im so confused in physics. say i toss a coin upwards. is the acceleration still -9.8m/s^2, since i applied force to it? or is the acceleration only -9.8m/s^2 if something is in free fall? aother example: if someone stood on the edge of a cliff and fired a gun straight downwards, is the acceleration -9.8m/s^2?

p.s. these questions are not my hw. i just came up with them as examples because i am so confused. thankyou!

Answer 1

After you release the coin, and after the bullet emerges from the gun, both the coin and the bullet are in free fall and the acceleration is -9.8m/s^2. You apply a force to the coin and the bullet, but one they leave your hand or the gun, that force is gone. The only force acting on them once they are in the air and freely falling is gravity.

Answer 2

The plus and minus signs are tricky. First, always pick a direction to be positive. Let's say that 'up' (away from the ground) is positive. With this notation, and can say that gravity always accelerates things 'downward', and therefore gravity is ALWAYS -9.8 m/s^2. When I work out a physics problem, any initial 'upward' velocity should be denoted as positive; 'downward' velocity is negative.



It does not matter which way the object is moving, as long as it undergoes freefall in a vacuum, it's acceleration is ALWAYS 'downward' at -9.8m/s^2. When the coin is moving 'up', it is slowing down, which implies the acceleration must be directed opposite the velocity - the acceleration is therefore 'down'. When the gun is fired straight down (in vacuum, mind you), the bullet will accelerate as it falls. So both the bullet's velocity and acceleration are negative, or 'downward'.



It's important to pick a sign convention - 'up' is positive - and keep with the same sign convention, for all quantities, throughout the entire problem.



Good Luck

Answer 3

Acceleration Of An Object

Answer 4

gravity has a force of 9.8 m/s, but you can round it to ten if you'd like. (i am learning this in physics) if you throw a ball upwards at 50 m, it will slow down 10 m/s each second it is in the air until it reaches zero (it will take 5 seconds to reach its peak). As it begins falling, it will gain 10 m/s every second it is falling until it hits the ground (assuming it is under the influence of gravity only, with no air resistance.) hope this helps.

Answer 5

the acceleration due to gravity is 9.8m/s^2

if you are throwing something up words its acceleration is opposing the real gravity and is there fore -9.8m/s^2 but when it is falling down the acceleration is 9.8m/s^2.



now when you fire a gun downwards its acceleration is not due to gravity. the gravity is helping it but the acceleration is because of the force caused by the combustion of fuel(gunpowder) in the bullet.

Answer 6

what's -9.8m/s^2? is that the force of gravity? I forget my physics!!

I believe that in a vacuum, where there aren't any other factors, yes the acceleration is like you said... but in real life, you have things like wind / friction that can affect the acceleration. Example is the feather vs penny in the vacuum... where they fall at the same rate.. but in the real world, you know that feather floats around a bit.