why in case of projectile motion the horizontal velocity remains uniform and the vertical velocity changes?

Answer 1

because gravity is a vertical force. since gravity constantly "pushes" the projectile downward, vertical velocity changes. there is no horizontal forces affecting the projecting, however, so no effect is done on the horizontal velocity. there is air resistance, etc., but that isn't taken into consideration for elementary physics

Answer 2

Total speed V = sqrt(Vx^2 + Vy^2); where Vx is the X component (horizontal) and Vy is the Y component (vertical). Vx is often considered constant because the problem question is discounting all forces on the projectile that act in the horizontal (X) direction. For example, in a real case, there would be drag forces as the projectile cuts through the air. But HS and early college physics questions usually ignore them to make the answer easier to come by. And to a point, even in the real case, the horizontal forces are often not significant; so they can be ignored if a lot of precision is not required in the answer. Vy on the other hand is caused by the one main force acting on a projectile after it leaves the muzzle...gravity. And as you probably know, the higher an object falls from, the faster will be its speed when the object strikes the ground. And, this is important, a projectile falls to the ground under the force of gravity just like any other object falling from some height. And the angle of the shot wrt the horizontal is a major factor in determining just how high above ground the projectile will go. This is easy to show.... Assume Vy = V sin(theta); where theta is that shooting angle. We can show that Vy^2 = 2gH; where H is the max height the projectile will go above the muzzle. Thus, H = Vy^2/2g = (V sin(theta))^2/2g and there you have it, H depends in part on sin(theta). For example, if the gun is pointing level with the ground, theta = 0 and H = 0 as a result. And if the gun is pointing straight up with theta = 90 deg, H = V^2/2g.

Answer 3

According to Newton's 1st law of motion every body continues in its state of uniform motion or rest unless it is compelled to change that state by an external impressed force. In a simple projectile motion there is only one force acting which is gravity that acts in the vertical direction.Since there is no force in the horizontal direction the velocity in this direction remains constant.

Answer 4

Newton’s first law of motion is ‘Every object is in its state of rest or of uniform motion unless compelled by an external force’


In the case of projectile motion, assuming no friction, the horizontal speed or velocity will change only if a force acts in its direction or opposite direction.
As there is no force in this direction its speed is not changing.

In the vertical direction the gravity pulls (gives a force) the object in the down ward direction. As a force acts in this direction, the speed changes in this direction.

Answer 5

The horizontal velocity is constant when we assume the frictional losses due to air to be negligible. However, same will be applicable to the vertical motion. But this velocity changes due to the gravitational force, acting reverse while going up and adding to while coming down.

Answer 6

Assuming there is no friction due to air, what you say is correct. The reason is that once you throw the object, there are no more forces acting on it in the horizontal direction. That is nothing is pushing the ball anymore. However, in the vertical direction gravity is pretty much in effect and that affects the ball's vertical velocity.

Answer 7

Good question. If there was no air resistance, nothing would slow down your horizontal motion; Newton's first law. It's a good approximation with a heavy projectile and reasonably low speeds. But gravity pulls you down vertically at an acceleration of 10 m/s^2, so you fall faster and faster, while you move forward at a constant speed.

Answer 8

The simple answer is that once the projectile is put in motion, there is no external force acting on the projectile in the horizontal direction and that there is a force (gravity) acting in the vertical direction.

Answer 9

Actually, it shouldn't. Air resistance will slow a projectile down, rifle bullets at the end of their course are much less powerfull as in the earlier part. The vertical velocity changes indeed, as was said above, because of gravity.

Answer 10

like most answered the vertical velocity changes because of gravity while the horizontal velocity remains uniform because it proves the law of inertia.