  Common misconceptions

Motion In A Plane

- What you are getting from a statement might not be necessarily true. Let's burst some of the common misconceptions
1
MYTH: At the top of its trajectory the velocity along with the acceleration of the object is zero. FACT: If you throw an object in the air it stops briefly(vertical velocity is zero) but acceleration is not zero (gravity doesn't stop) its role is to change the direction of velocity vector If we have a look at the horizontal and vertical velocity vector from the parabolic flight one can see that there is some horizontal motion still at the peak and acceleration due to gravity at peak.  2
MYTH: Greater the angle of projection, greater the range of projectile. FACT: Range of projectile is maximum at angle of projection 45 degree The range of a projectile depends on the angle of projection as well as the component of horizontal velocity. But the maximum range is obtained only when the projectile is thrown at an angle of from the horizontal. It is explained in the image attached below.  3
MYTH: In uniform circular motion the acceleration is zero, as particle is moving with constant velocity. FACT: The particle is moving at constant speed but not constant velocity, the direction of the velocity is changing continuously, that's why acceleration is not zero.
The rate of change of direction is centripetal acceleration, objects moving with constant velocity in circular motion have constant acceleration as the velocity of the object keeps on changing due to change in its direction of motion.
4
MYTH: Showing the parabolic nature of projectile leads the students to believe that they are different from linear motion or from horizontal motion. FACT: The projectile motion is simultaneous horizontal and vertical motion. The x part of motion occurs exactly as it would if the y- part did not occur at all. Similarly, y part of motion occurs exactly as it would if the x part of motion did not occur.
The projectile motion is only the combination of the horizontal and vertical motion of a body at each and every point of its motion. But for calculation, when we consider horizontal and vertical motion separately, they are only the individual straight line motions.
5
Three people crossing a river as shown in figure, which one will cross the fastest.
MYTH: C is moving forward, C will also be moving along with the current, two positive direction motion = faster velocity. C will get their first because it is using the current to its advantage FACT: B will reach the shore first The person B will reach the other end first because his vertical component of the velocity is greater than that of the others. The key here is how fast the vector in the vertical direction is because the distance is to be covered in vertical direction.  