Scalar quantities: Time - Scalar quantities often refer to time; the measurement of years, months, weeks, days, hours, minutes, seconds, and even milliseconds. Volume - Scalar quantity can refer to the volume of the medium, as in how much of the medium is present. Everything from tons to ounces to grams, milliliters and micrograms are all scalar quantities, as long as they are applied to the medium being measured and not the movement of the medium. Speed and temperature - Two more commonly used scalar quantities in physical calculations are speed and temperature. As long as they are not associated with a directional movement, they remain scalar quantities. For instance, the measurement of speed in miles or kilometers-per-hour or the measurement of the temperature of the medium both remain scalar quantities as long as they aren't associated with the direction of the medium's travel.
Vector quantities: Time - Scalar quantities often refer to time; the measurement of years, months, weeks, days, hours, minutes, seconds, and even milliseconds. Volume - Scalar quantity can refer to the volume of the medium, as in how much of the medium is present. Everything from tons to ounces to grams, milliliters and micrograms are all scalar quantities, as long as they are applied to the medium being measured and not the movement of the medium. Speed and temperature - Two more commonly used scalar quantities in physical calculations are speed and temperature. As long as they are not associated with a directional movement, they remain scalar quantities. For instance, the measurement of speed in miles or kilometers-per-hour or the measurement of the temperature of the medium both remain scalar quantities as long as they aren't associated with the direction of the medium's travel.
Regardless of the initial velocity of the pebble, the acceleration of the pebble is equal to the gravitational acceleration which is equal to 9.8 m/s2 towards downwards direction.
This can be shown by Newton's Second Law. According to the law, the net force applied on an object is equal to mass times acceleration of that object.
During the downward motion, the only force acting on the pebble is the gravitational force, hence its acceleration is equal to gravitational acceleration.
