Re: Newton's 2nd law Lab

[Herbert H Gottlieb <herbgottlieb@JUNO.COM>]

I cannot understand the comments of the parent
that transferring mass from the cart to the hanging
weight affects the amount of mass that is accelerating.

The entire system in motion consists of a cart on a
horizontal table and a string which passes over a
"frictionless-massless" pulley with a hanging mass
(weight) fastened to the string at the lower end that
supplies an accelerating force. (Force probe???).

The applied force that accelerates the system acts
on both the hanging mass and the mass of the cart
simultaneously. Therefore the magnitude of the
acceleration of the cart must equal the magnitude
of the acceleration of the hanging mass.

Since the cart is accelerating in a horizontal direction
and the hanging mass is accelerating in a vertical
direction, the directions of the accelerations are
different but their magnitudes must be exactly equal.

This lab experiment appears in my book "Experiments for
Physics Labs" currently published by Analog Press.

Herb  Gottlieb from New York City
(Where masses that are tied together accelerate together)

On Wed, 09 Dec 1998 22:35:04 -0600 Norman Lohstreter <petel@TENET.EDU>
writes:
> I had a parent question the procedure for verifying Newton's second
> law.  The procedure involves a cart with added mass and a force probe
> which is connected by a massless cord that passes over a
> massless/frictionless pulley to a smaller hanging mass that provides
> the
> force.  The standard procedure (from several lab manuals) says to
> take
> mass from the cart and transfer it to the hanging mass position in
> order
> to keep the mass of the system constant.  This seemed to make sense
> to
> me until the conversation with the parent.
>
> His position was, the only mass that was necessary to keep constant
> was
> the mass on the cart and if you transfered the mass from the cart to
> the
> hanging position, you were changing both the accelerating mass and
> the
> applied force and that there was no way to determine the results you
> wanted because there were too many variables.
>
> Since the force is being measured by the force probe connected to the
> cart/mass component, is it still necessary to keep the mass of the
> system constant?  We now are able to measure the accelerating force
> acting on the cart itself. The force acting on the hanging weight is
> different from the tension in the cord because the hanging weight is
> accelerating too.  There is much similarity to the attwood machine
> here.
>
> Any assistance is greatly appreciated.
>
> Pete Lohstreter
> NGHS