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SHM · Lecture 13 of 26

Stacked blocks in SHM: when does the top block slip or lift off?

By Lalit, IIT Madras

Stacked blocks in SHM for JEE Advanced: the friction the top block needs, the normal force on a block moving up and down, and lift-off.

Watch lecture 13

Chalkboard titled "Two blocks, one spring": a small block m rests on a larger block M that is joined to a wall by a spring (k > 0) on a floor, a red arrow marks friction on the top block, and the boxed formula reads friction = m|a| = mkx/(M + m).

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What this lecture covers

Two blocks on one spring move as one system, and static friction gives the top block its share of the acceleration. That acceleration peaks at ω² A at the extremes, so slipping starts there and limits the amplitude. For a block riding a plank up and down, the normal force is greatest at the bottom. Blocks on a standing spring are likeliest to part at the highest point, and a heavy floor block lifts once the spring above it is stretched enough.

In this lecture

  1. Play from SHM so far, and today's three questions
  2. Play from Two blocks on a spring, static friction
  3. Play from A rough plank: when does the block slip
  4. Play from The normal force only pushes
  5. Play from Normal force N and when the block leaves
  6. Play from Two blocks on a standing spring
  7. Play from The top block can only be pushed
  8. Play from A spring standing on a heavy block
  9. Play from Amplitude before the floor block lifts
  10. Play from Recap: slipping and lifting off