Newton's Second Law of Motion.. i have a question on this. please help me.?

Question

from Newton's Second Law of motion, the acceleration is proportional and in the same direction as the "net" force. Does this mean that the direction of acceleration is in the direction of motion? please explain this to me..

Answer 1

No, it is not necessary that direction of acceleration is direction of motion.

Consider two examples.

1) Projectile motion: - Here acceleration, which is acceleration due to gravity, is always vertically downward but the object is moving on a projectile path.

2) A particle moving with constant speed on a circular path. At any point, the motion is along tangent to the circle at that point. But acceleration is towards centre and is called as centripetal acceleration.

Answer 2

If you throw a ball straight up in the air the 'net' force (neglecting air resistance) due to the weight of the ball is straight down and the acceleration due to gravity is also straight down.  At first the acceleration is in the opposite direction of motion which slows, stops and reverses the direction of motion causing the ball to fall.  The direction of acceleration is in the direction of net force.  

Answer 3

Motion will be in the same direction as the "net" force.

Answer 4

The first answer is not necessarily correct, first of all we must understand that the velocity of an object is a vector as opposed to a scalar (unlike speed) this means that the direction of motion is built in to the value. the net force affects the velocity of the mass by accelerating it if the value is positive or decelerating it if it is negative.

0--------->  V    <--------F

the object moving to the right here is subjected to a force and therefore an acceleration opposite to it's motion the objects will continue moving opposite to the force until it's velocity is reduced to below zero at which point it will move to the left

Answer 5

No.

The direction of acceleration is the same as the direction of the net force. In some situations, direction of net force may be opposite to the motion in which case, direction of acceleration will be opposite to the motion. For example, when brakes are applied to a moving vehicle, net force is opposite to the motion. So acceleration is opposite to the motion meaning the vehicle is decelerating.

Answer 6

No

think of orbit - force and acceleration are towards the earth - motion at right angles to it.

Net force must be co linear with net acceleration.  not motion.