Download Mass vs. Weight

Mass vs. Weight
All matter has mass. Mass is a measurement of how much matter you have.
Mass is a physical property of everything that exists in the Universe. No matter where you are or what you are
doing, your mass at any given moment in time remains the same. For example, if you are standing on the Earth
and you have a mass of 45 kg, your mass would be the same if you somehow instantaneously traveled to the
Moon.
Your mass can change over time, however. For example, if you eat three cheeseburgers every day for a month,
your mass will change because you will add more matter to yourself. It is important to note, however, that the
overall mass of the Universe does not change. According to the law of conservation of matter, the total amount of
matter cannot change; it can only change forms. In this case, it changed from a cheeseburger into fat cells on your
body.
Weight is different from mass because weight depends on gravity.
Unlike mass, your weight can change in an instant depending on where you are located. For example, if you are
standing on the Earth and you have a mass of 45 kg, your weight would be approximately equal to 440 N (100
lbs).
45 kg x 9.8 m/s2, where 9.8 m/s2 is the acceleration due to gravity on the Earth
On the Moon, however, your weight would only be 72 N (16 lbs) because there is less gravity on the Moon than
there is on Earth.
45 kg x 1.6 m/s2, where 1.6 m/s2 is the acceleration due to gravity on the Moon
W=mxg
weight = mass x acceleration due to gravity
Gravity in the Solar System
Gravity is a force among all objects in the universe. Within our solar system, every object is attracted to every
other object due to gravity. The closer objects are and the more mass they have, the stronger the attraction.
Gravitational forces among objects in the solar system cause distinct characteristics, such as tides and varying
orbital motion and speed.
The Influence of Mass on Gravity
The greater the total mass of two objects, the greater the gravitational force between them. For example, a
meteoroid positioned halfway between two asteroids will be attracted more to the asteroid with the greater mass.
The difference in mass between two objects can also affect how gravity affects the objects' motion. The motion of
the less massive object is more affected by the force than is the motion of the more massive object. For example,
the planet Jupiter is much more massive than its moons. This is why each of its moons orbit around the planet.
The gravitational force between Jupiter and its moons does affect the motion of Jupiter, but only slightly.
Another example of this is the orbits of all the planets around the Sun. The Sun is the most massive object in the
solar system. This causes all the planet-moon systems, asteroids, meteoroids, and comets to orbit around the Sun.
The Sun moves only slightly due to the gravitational force between it and the planets. Because of this, the Sun
stays in the central part of the solar system while the planets move in large orbits around it.
The Influence of Distance on Gravity
The shorter the distance between two objects, the stronger the gravitational force between them. For example,
because the Moon's orbit is elliptical, the gravitational force between the Earth and the Moon is stronger when the
Moon is closer to the Earth. When the Moon is farther away in its orbit, the gravitational force between it and the
Earth is weaker.
Distance vs. Mass
Both distance and mass influence the gravitational force between two objects at the same time. Differences in
distance have a greater effect on gravity than do differences in mass. For example, the gravitational force
between the Earth and the Moon is stronger than the force between the Earth and the Sun. Even though the Sun
has such a great mass, the shorter distance between the Earth and the Moon makes the force between the Earth
and the Moon much stronger than the force between the Earth and the Sun.
Gravity & Tides
Tides are a rhythmic rising and falling of a solar system object's surface due to gravity between the object and
some other object. The Earth has tides mainly due to the gravity between the Earth and the Moon, but the gravity
between the Earth and the Sun influences the tides as well. The Moon has a greater effect on the Earth's tides
than the Sun because the Moon is so much closer.
Tides are at their highest and lowest (spring tides) when the Earth, Moon, and Sun line up, and they are at
moderate levels (neap tides) when these bodies form a right angle. These variations in tide levels are especially
apparent in Earth's oceans.
Gravity & Planetary Orbits
The gravitational force between a planet and the Sun, along with the planet's continual forward motion, keeps the
planet moving in orbit around the Sun. Each planet's orbit is shaped like an ellipse, which is a special kind of
oval.
This gravitational force also determines the planet's orbital speed. The gravity between planets and the Sun is
stronger for planets closer to the Sun than for planets farther away from the Sun. And, the stronger the force, the
faster the orbital speed.
Electricity and Magnetism
Electricity and magnetism are integrally part of each other.
Permanent Magnets
A permanent magnet is a material that produces a magnetic field without any external magnetic field being
present. Permanent magnets can be demagnetized by heating them past the Curie point.
Every magnet has both a north pole and a south pole. The magnetic field around a bar magnet is shown below.
If two magnets are placed so that a north pole and a south pole are facing each other, they will attract each other.
If two magnets are placed so that two south poles or two north poles are facing each other, they will repel each
other. This is shown below.
Electromagnetism
Electricity and magnetism are two different parts of the same phenomenon. An electric field cannot exist without
a magnetic field and vice versa.
When a current is moving along a wire, a magnetic field is generated. The magnetic field increases when a current
is moving along a coiled wire. When the wire is coiled around a core made of a material that is easily magnetized,
the strength of the magnetic field increases further. A magnetic field can also be strengthened by increasing the
number of coils or increasing the current.
Just as electric current generates a magnetic field, a magnetic field also generates an electrical current. An electric
generator creates a moving magnetic field by using mechanical energy to move a magnet. The changing magnetic
field then generates an electrical current.
Movement of Electrical Charges
Magnetism also affects electrically charged particles. For example, a charged particle moving into a magnetic
field will be bent from its path.
The orientation of a magnetic field also depends on the direction of current flow. The magnetic field is always
perpendicular to the current flow.
Electromagnets
An electromagnet is an object that behaves like a magnet, but its magnetic force is a result of an electric current.
A simple electromagnet can be built by creating an electrical circuit between a battery and a wire coil (also called
a solenoid) wrapped around an iron core. A single loop of wire carrying a current does not have a very strong
magnetic field. However, if many loops are used to form a coil, the magnetic fields of the loops add together to
make a much stronger magnetic field.
When the current is turned off, the iron loses its magnetism. The strength of an electromagnetic field is
determined by the amount of current, the number of coils of wire and the distance of the coils from the iron.
Below is a picture of an electromagnet: