Question

Physics❤️

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Acceleration goes on decreasing with time but it is not retardation.

please explain this statement.​

Answer 1

What retardation actually means is merely 'negative acceleration'. Here the term 'negative' corresponds to the direction of the acceleration.

If we consider the direction of motion of a body as positive direction but the acceleration is occurring in the body in the opposite direction, i.e., in the negative direction, then the acceleration is known by the term 'retardation' in this case.

A simply example is given below. Consider a ball projected vertically upward. Here the upward motion is usually considered as positive. But the acceleration acting on this ball, here (assuming no other external force is acting on the ball), is nothing but the acceleration due to gravity, which is acting downwards, i.e., in the negative direction. So, in this case, the acceleration due to gravity is retardation with respect to the ball.

Only the acceleration in the negative direction is called as retardation. The decrease in the magnitude of the acceleration doesn't let us call it retardation. That's the important matter.

In the velocity - time graph, since the slope or tan θ decreases with time, it means that the magnitude of the acceleration is gradually decreasing and tending to zero, but the acceleration doesn't become less than zero. Thus it is not a retardation.

To show the retardation, the graph should curve downwards. But here the graph is tending to be a straight line, which means that acceleration tends to be zero.

Answer 2

Dᴇᴄᴇʟᴇʀᴀᴛɪᴏɴ ɪs ᴡʜᴇɴ ʏᴏᴜʀ ᴠᴇʟᴏᴄɪᴛʏ ᴅᴇᴄʀᴇᴀsᴇs ɪɴ ᴍᴀɢɴɪᴛᴜᴅᴇ. Iғ I ᴀᴍ ᴛʀᴀᴠᴇʟʟɪɴɢ ᴀᴛ , ᴀɴᴅ ᴛʜᴇɴ 1 sᴇᴄᴏɴᴅ ʟᴀᴛᴇʀ, I ᴀᴍ ᴛʀᴀᴠᴇʟʟɪɴɢ ᴀᴛ , ᴛʜᴇɴ I ᴀᴍ ᴅᴇᴄᴇʟᴇʀᴀᴛɪɴɢ ᴀᴛ (ᴏɴ ᴀᴠᴇʀᴀɢᴇ). Dᴇᴄʀᴇᴀsɪɴɢ ᴀᴄᴄᴇʟᴇʀᴀᴛɪᴏɴ ɪs ᴡʜᴇɴ ʏᴏᴜʀ ᴀᴄᴄᴇʟᴇʀᴀᴛɪᴏɴ ᴅᴇᴄʀᴇᴀsᴇs ɪɴ ᴍᴀɢɴɪᴛᴜᴅᴇ.