Hi, visitor! Register | LoginJoin Hire Faqs

Kids Modeling Agency
202, Mayur Plaza, Samachar market,
Mayur Vihar 1 extn., Delhi

FaceBook | Instagram | G+ | Twitter

Elevator Physics

Kids Learning October 1, 2013

Elevator Physics

You get into an elevator (or a lift, as we sometimes call it) and for a second or two, just as the elevator moves down, we feel weightless. On the other hand, if we go up in an elevator, we suddenly feel heavier just as the elevator lurches upwards.
To understand this feeling of weightlessness, we need to understand a few basic things first.

Mass: The amount of matter that constitues us results in our mass. Mass is the property which “resists” a change in acceleration (linear or angular). It is this “resistance” that results in inertia.

Weight (or Actual Weight): When gravity acts on matter (our body), you have a weight (actual weight). But this, theoretically, means that actual weight can only be computed when you consider all the gravities from all the different bodies in the universe acting on the mass. The sum of all these gravities is equivalent to the net gravitational force or the gravitational field (which is not necessarily the same as ‘g’ of the ‘free fall acceleration’). Actual weight only depends on the net gravity and the mass it is acting on.

Apparent Weight: As opposed to actual weight, apparent weight is what your weighing machine shows you. When you are standing on a platform, and that platform is neither going up nor down with respect to the earth (whose gravitational field basically dominates every other graviational field), the platform pushes up against your feet in the opposite direction of the earth’s gravity. This “pushing you up” by the platform is what enables you to stand “on” the platform. Your actual weight is — always — gravity acting on your mass. But your apparent weight is the “opposite, pushing-up force’ applied by the platform. Therefore if you are standing on a weighing scale, this opposite force is what the weighing machine can measure.

Weightlessness: This is actual weightlessness, and corresponds to actual weight — and this occurs when no gravity acts on your body’s mass, which is an impossible situation in the universe.

Apparent Weightlessness: As opposed to actual weightlessness, apparent weightlessness occurs when your apparent weight zeros out. Now, if you remember, apparent weight was the opposite, pushing-up force applied by the platform or the weighing machine on which you were standing.

However this opposite force is not always equal to the actual weight. When does such a strange thing happen? Here are two examples. Suppose you are floating in a tub full of water, and try to stand on a weighing machine on the floor of the tub. Though your actual weight remains unchanged, since the buoyancy of the water in the tub exerts an upward force on your body, you can no longer “press” down with as much force as earlier on the weighing machine. This is why the weighing machine will register a lighter apparent weight.

In the second example, consider that the platform, on which sits the weighing machine, on which you are standing, begins to fall down at terminal velocity, so that you, the scale and the platform are all falling at the same velocity towards the earth. (For a definition of “terminal velocity”, please go to the end of this article). Now you can no more practically “press” down on the weighing machine, therefore it will register nothing. Your apparent weight has zeroed out and you are in apparent weightlessness. This is what happens to astronauts too in a spaceship orbiting the earth. However you still have actual weight.

Conversely had the platform suddenly started climbing upward away from the earth, then you would “press” down harder on the weighing scale for a moment before all the velocities equalized, and the weighing scale would register a higher apparent weight. It’s not as if you really gained a couple of pounds by stepping into the elevator!!

So the key concepts to grab are the definitions of weight or actual weight, and the meaning of apparent weight. An experiment on an elevator with a bathroom weighing scale can drive the point home.

To conclude (quoting from wikipedia: http://en.wikipedia.org/wiki/Apparent_weight ):

An object’s apparent weight is equal to its actual weight, except if:
• The object has an acceleration, as in a lift, a rocket or a rollercoaster.
• Some force other than the earth’s gravity and the normal force is acting on the object. This may be buoyancy, magnetic force, or the gravitational force of another body.

Terminal Velocity: The velocity when a falling object is no longer accerlerating; the force due to gravity is equal to the opposing force of air resistance.. When an object continues to fall steadily until air resistance becomes so great that it equals with the pull of gravity and the object can fall no faster.

No Tags

813 total views, 1 today

  

  • Modelling Agency for Kids

    Kids Modelling Agency

    by on September 12, 2013 - 0 Comments

    Kids talent & modelling agency is a company that represents kids talent, child models, kid models, toddlers, babies, pre teen models, teen models to work for the fashion, entertainment and modelling industry. A child model or a kid model refers to a child who is employed to advertise , display and promote commercial products or […]

  • Kids modelling agency in Delhi

    Create the Best Modelling Portfolio

    by on May 9, 2014 - 3 Comments

    Metropolitan cities Mumbai and New Delhi are the hubs for kids modelling in India. Due to this, the best modelling portfolio, whether for child or adult, can be created in either of the two cities. Most of the well known fashion designers, top production houses and models are present in this city, as a result […]

  • Toys

    by on October 28, 2013 - 0 Comments

    Toys Its time for toys. Kids all time favorite toys are being manufactured by popular toy makers. Toys for little boys are somewhat different from the little girls toys. Hot toys are fun to play with and they are always ready to entertain kids with their uniqueness. Lets find out such toys. Fisher-Price T.M.X. Elmo, […]

  • Mickey Mouse

    by on October 18, 2013 - 0 Comments

    Mickey Mouse Mickey Mouse – the one mouse anyone would love to have scurrying about their house, is undoubtedly the most popular cartoon character to date. Did you know that the creation of Mickey Mouse is what made Walt Disney so successful? When Walt was 26 years old, he was returning home by train with […]

  • Footwear Facts

    by on October 28, 2013 - 0 Comments

    Footwear Facts Sandals originated in warm climates where the soles of the feet needed protection but the top of the foot needed to be cool. 4,000 years ago the first shoes were made of a single piece of rawhide that enveloped the foot for both warmth and protection. In Europe pointed toes on shoes were […]