Message-Id: <l03102800b0ad49931086@[209.142.5.89]>
In-Reply-To: <n1330928643.9761a@Tesla.exploratorium.edu>
Date: Thu, 4 Dec 1997 23:37:56 -0700
To: pinhole@exploratorium.edu
From: Ron Wong <ronwong@inreach.com>
Subject: Re: vector components
On 3 Dec 1997 12:25:20, U
geoff ruth <geoffr@eastside.org> said:
>
>Wait! I'm confused too -- I'm with your kids. I think that gravity does
>pull only straight down. I think that the reason that the ball (or whatever
>it is on the ramp) is moving at an angle is because the ramp is exerting a
>normal force perpendicular to the surface of the ramp. When you do vector
>addition to combine these two forces, then you get something that points in
>the direction the ball actually moves. .....
>
>Let me know where __my__ confusion lies.
>
There is no basis for any confusion here, Geoff. You're right.
Assuming there is no friction, the only forces acting on the object is the
normal force and the force of gravity which, as the kids kept pointing out
to Steve, is always acting straight downwards. The vector sum of these two
forces is the net force. It is this net force acting down the incline plane
that leads to the observed acceleration of the object down the plane.
Traditionally, many teachers approach this problem by breaking up the force
of gravity into two components - one perpendicular to the plane and one
parallel to the plane. The net force is now the sum of three vectors - the
two components and the normal force. When taking this sum, the
perpendicular component of the force of gravity cancels out the normal
force (there is no motion in this direction so Newton's Law of Inertia
requires that the sum of these two forces be zero). This leaves just the
component of gravity parallel to the incline plane. Since it's an
unbalanced force (it's the same as the net force arrived at by adding the
normal force to the force of gravity in the preceding paragraph), it leads
to the acceleration of the object down the plane.
To each his/her own. - ron