Question

Is this acceleration? Give reason.

i)A car is going at a constant speed in a straight line. 

ii)Dropping a pebble into water

iii)Catching the ball

iv)Throwing a ball in the upward direction

v)Ball moving in a circle at constant speed.​

Answer 1

1. The acceleration of a car that travels in a straight line at a constant speed of 100 km/h is zero. Average acceleration = (change in velocity)/(time it takes). Since the car's change in velocity is zero, its acceleration is zero.
2. “Drop a pebble in the water: just a splash, and it is gone; But there's half-a-hundred ripples circling on and on and on, Spreading, spreading from the center, flowing on out to the sea. And there is no way of telling where the end is going to be.
3. Advancing or retreating so as to maintain a projectile's constant vertical optical velocity was suggested by Chapman (1968) as a possible basis for locomotion in ball catching. Three experiments examined this thesis. In Experiments I and 2, the positions of balls and catchers were videotaped to see if the movements of the catchers canceled optical acceleration. Such canceling was indeed observed until just prior to the catch for hand-thrown balls (Experiment 1). The monocular availability of the information predicts success with monocular viewing, confirmed in Experiment 2 with machine-thrown balls. In Experiment 3, observers judged whether a ball (represented as a moving dot on a computer screen) would land at, in front of, or behind them. Performance was above chance, but only some observers used acceleration. Together, the experiments provide broad, though not unequivocal, support for the utilization of optical acceleration to guide locomotion in catching.
4. During ascent ball is going upward therefore its position is positive. Now , though the velocity is decreasing but its direction is upward i.e. positive. Ball is moving under the effect of gravitational acceleration , which is always acting vertically downwards so it is negative.
5. For this reason, it can be safely concluded that an object moving in a circle at constant speed is indeed accelerating. It is accelerating because the direction of the velocity vector is changing.

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