The document summarizes how three different objects work: 1) Phonograph needles vibrate as they run through grooves on records, generating electrical signals that are amplified and converted to sound. 2) Golf ball dimples reduce drag by allowing air to cling to the ball's surface longer, and create lift by carrying air faster over the top of the spinning ball. 3) Light bulbs have a rounded shape that distributes gripping force over a wide area through curvature, preventing excessive stress at any point.

2. • The needle or stylus is an artificial sapphire
or diamond with a rounded or elliptical tip.
The grove is a different shape each side, one
for the right hand stereo and one for the left-
hand signals.
The needle vibrates as it runs along the
uneven groove walls, setting up electrical
signals in the pick-up head. The signals are
then amplified and then converted to sounds
by cones (diaphragms) vibrated by
electromagnets in the loudspeakers.

4. • When a ball is in flight, a thin layer of air clings to its
surface at the front. As the air passes over the ball, it
breaks away from the surface setting up turbulent
eddies behind. The eddying air draws its energy from
the ball, slowing it down. Dimples cause the air to
cling to the surface until it is well towards the rear of
the ball. When it finally breaks away a narrower
stream of turbulence is created causing less drag than
for a smooth ball.
The dimples have another purpose as well. Since the
golf ball always spins backwards when it is struck, the
dimples carry air upwards over the top. The air going
over the top has to travel faster than the air going
underneath because of this rotation. This creates a
lower pressure above than below, so the ball
experiences lift which keeps it in the air longer.

6. • The explanation for this lies mainly in the
bulb’s shape which exploits the eggshell
principle. Light bulbs and eggs have a
rounded profile over the whole surface.
When you grip a bulb, the force you apply is
transmitted in all directions away from the
point of contact by the curve of the glass.
This result in the force being distributed over
a wide area, and no excessive stress being set
up at any point.