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velocity
if moving with constant velocity the only force to slow it down is kinetic friction; if it is accelerating velocity is not constant and an additional force is being applied.
Never.Average velocity is total displacement (final position minus initial position) divided by the total time: vave = (xf-xi)/tAcceleration is the rate at which your velocity is changing or change in velocity over time: a= (vf-vi)/tThese two quantities may have the same numerical value but will never have the same units.Average velocity for a trip can equal instantaneous velocity at a certain point during the trip, however, at any time during a trip in which the velocity is constant or at half way through the total time of a trip where the acceleration is constant.
The book slides with constant velocity.
Not necessarily. Impulse Fdt=change in momentum which could be written as mdv (constant mass, velocity changing) or dmv (changing mass, constant velocity - the so-called conveyor belt problem. Imagine a hopper filled with (say) coal is feeding the coal on to a conveyor belt. The mass of the belt increases with time, so a force has to be applied to it to keep it moving at constant velocity.
velocity
if moving with constant velocity the only force to slow it down is kinetic friction; if it is accelerating velocity is not constant and an additional force is being applied.
If the box is sliding along at a constant speed, the net force acting on the box is zero.If the net force was not zero, the box would either be speeding up or slowing down.Non-zero net forces acting on objects cause the objects to accelerate. Therefore, if the net forces is not zero, the velocity of the object could not be constant.
Never.Average velocity is total displacement (final position minus initial position) divided by the total time: vave = (xf-xi)/tAcceleration is the rate at which your velocity is changing or change in velocity over time: a= (vf-vi)/tThese two quantities may have the same numerical value but will never have the same units.Average velocity for a trip can equal instantaneous velocity at a certain point during the trip, however, at any time during a trip in which the velocity is constant or at half way through the total time of a trip where the acceleration is constant.
The book slides with constant velocity.
friction
No, not at all. As long as a constant force is applied, the velocity can continue to grow or shrink.
Frictional force is applied when:you are walkingyou are holding an itemyou are writing
Certainly not. An object has momentum on account of its motion, which depends on its mass and its velocity. Force may be involved in the object's motion, but doesn't need to be. If we let the discussion become somewhat flabby, we can imagine a constant force applied to an object, and asked what happens to the object's momentum. An object with a constant force acting on it exhibits constant acceleration in the direction of the force. In that situation, the object's speed, and therefore its momentum, are proportional to the time the force continues to act on it.
In Simple motion, there is no force being applied. The moving object moves in a straight line with constant velocity. In acceleration, there is a force applied. The object's velocity is changing. The first derivative of acceleration is velocity. The first derivative of velocity is distance. (Derivative is a calculus thing.)
Not necessarily. Impulse Fdt=change in momentum which could be written as mdv (constant mass, velocity changing) or dmv (changing mass, constant velocity - the so-called conveyor belt problem. Imagine a hopper filled with (say) coal is feeding the coal on to a conveyor belt. The mass of the belt increases with time, so a force has to be applied to it to keep it moving at constant velocity.
Newton's First Law of Motion states that an object remains at a constant velocity unless it has an unbalanced force acting upon it. That constant velocity includes zero, which means that a stationary object with no force applied to it will not move. Since velocity includes direction, then a moving object with no force applied to it will continue to move in a straight line at a constant speed.That tendency is called inertia.