Simulation · Physics · Class 11
Heavier or lighter in a lift?
From the lesson Common forces in mechanics in Laws of Motion. Change the values and watch what happens.
Heavier or lighter in a lift?Physics · Class 11
The idea behind it
NCERT § "Common Forces in Mechanics"
- Gravity acts at a distance; all other everyday mechanical forces are contact forces that arise where bodies touch.
- The normal reaction is the component of a contact force perpendicular to the surfaces in contact; it adjusts to whatever value prevents the bodies from passing into each other.
- Tension is the pull transmitted by a string. For a light (massless) inextensible string over a frictionless pulley, the tension is the same all along it.
- A spring exerts a restoring force F = −kx for small extension or compression x, where k is the spring constant; the negative sign shows it opposes the deformation.
- In a lift accelerating upward at a, a person's apparent weight (the normal force from the floor or the scale reading) is m(g + a); accelerating downward it is m(g − a).
- A lift moving up but slowing down has downward acceleration, so the scale reads less than mg. The direction of acceleration matters, not the direction of motion.
- In free fall (a = g downward) the scale reads zero; the body appears weightless though gravity still acts on it.