Page 322 - (DK) The Ultimate Visual Dictionary 2nd Ed.

PHYSICS AND CHEMISTR Y
Force and Single-pulley system SIMPLE MACHINES Four-pulley
system (compound
Two-pulley system
(simple pulley)
pulley)
(simple pulley)
Pulley wheel
motion Simple pulley only changes Pulley wheel Two pulley
wheels
direction of a force
FORCES ARE PUSHES OR PULLS that change the Effort is the
Effort is
motion of objects. To make a stationary object same size as the half the load Effort is
load (10 N) and one quarter
move, or a moving object stop, a force is needed. (5 N), but the
is pulled the of the load
A force is also required to change the speed or same distance rope must be (2.5 N), but
pulled twice
direction of an object. This change in speed or the distance the rope
One rope must be
direction is known as acceleration. Acceleration depends
attached pulled four
on the size (magnitude) of the force, and on the mass of to load Two ropes times the
the object. The effects of forces were first summarized by share the distance
Load force and
Isaac Newton in his three laws of motion. The international
of 10 N distance Four
unit of force, named after him, is the newton (N), which is ropes
Pulley share the
approximately equal to the weight of one apple. Gravity—the force of
wheel force and
attraction between any two masses—can be measured using a newton distance
meter (spring balance). Forces are put to useful effect in machines. A
simple machine, such as a wheel and axle, is a device that changes the
size or direction of an applied force. It allows an applied force (the effort) Load
to produce another force (the load). A lever uses a bar that turns on a of 10 N
fulcrum to exert force. In all simple machines, there is a relationship
SIMPLE AND COMPOUND PULLEYS
between force and distance. A small force (in a compound pulley, for
instance) moves through a large distance to lift a heavy object Two
pulley
a small distance. This is called the Law of Simple Machines. wheels
NEWTON METERS (SPRING BALANCES)
Pedal
Wheel and axle Load
Weight is measured multiplies the effort of 10 N
using a spring
Effort, provided by
When weight pulls Force is transmitted cyclist’s muscles, is
downward, pointer to the wheels by the chain smaller than the load,
moves along scale Crank but moves through a
and measures force greater distance
A larger force,
the load, is
Weight is 10 N produced
WHEEL AND AXLE
at the axle
Weight is 20 N Effort, a
A screw, acting like turning force
a wedge wrapped supplied Effort Ax blade has
around a shaft, through a pushes ax wedge shape
multiplies the effort screwdriver into wood
Wedge
Mass of 1 kg Pitch multiplies
(the angle A larger effort
of the screw force, the
thread) load, moves
Mass of 2 kg The smaller the through
angle of pitch, a smaller
WEIGHT AND MASS the less force is distance to
The “mass” of an object is a measure of the required, but A larger push wood
quantity of matter that it possesses. Mass is more turns are force, the apart
usually measured in grams (g) or kilograms needed to move load, pulls
(kg). The “weight” of an object is the force it through a the screw
exerted on the object’s mass by gravity. Since greater distance into wood
weight is a force, its unit is the newton (N). SCREW WEDGE
320