2. Introduction of motion
Forces
Laws of motion
Gravity
Velocity
Acceleration
3. Everything in the universe moves.
Question: if you are sitting still at your
desk, are you moving?
Answer: Yes. You are on Earth. The Earth
is moving around the Sun. The Sun is
moving around our galaxy.
4. Forces need to act upon an object to
get it moving or to change its motion.
Forces could be big or small.
Big forces: the pull of a star on a planet
Small forces: the pull of a nucleus on an
electron.
5. Scientists measure forces in units called
Newtons (N).
Example: you kick a soccer ball with a
force equivalent to 12 N. The force of
gravity causes the ball to return to the
surface.
6. Gravity or
gravitational forces
are forces of
attraction.
Every object in the
universe that has
mass exerts a
gravitational pull, or
force, on every other
mass.
7. Sir Isaac Newton came up with the three
basic ideas that are applied to the physics of
most motion.
Scientists now call them Newton's Three Laws
of Motion.
8. An object at rest tends
to stay at rest, and an
object in motion tends
to stay in motion, unless
acted upon by an
unbalanced force.
That is, objects tends to
keep on doing what
they're doing!!!
11. The third law says
that for every action
(force) there is an
equal and opposite
reaction (force).
Forces are found in
pairs!
12. Velocity is word used describe if a
motion is fast or slow. That is, velocity is
the rate of motion in a specific direction.
Question: if you are walking 5 km/hour.
Would you say that you know your
velocity?
Answer: No. You only know your walking
speed. Your velocity would be if you are
walking 5 km/hour north (or S/W/E).
13. Question: A car
travels 420 km in 4
hours from Alicante
to Madrid. What is its
velocity?
Velocity = 105 km/h
Alicante-Madrid.
14. When velocity changes, the word
“acceleration” is used.
Acceleration is also a vector. That is, the
direction needs to be specified.
15. There are a few
special situations
where acceleration
may be constant.
This type of
acceleration
happens when there
is a constant net
force applied. The
best example is
gravity.
16. The acceleration of an object due to
gravity is constant near the Earth´s
surface. Do you know its general value?
G = 9.82 m/s2
17. In a vacuum (el vacío), which
would fall faster: a feather or a ball
of the same mass?
Answer: they would fall at the
same rate in a vacuum.
Note: in real life, there is air all
around us. When a feather falls, it
falls slowly because the air is in its
way. There is a lot of air resistance
and that resistance makes the
feather move slower.
18. Do you think that gravities (or gravitational
forces) on other planets are the same on
Earth?
The gravities of other planets are different
from Earth's gravity because they may have
different masses and/or sizes. Even though
the gravity may be smaller or larger, it will
still create a constant acceleration near the
surface of each planet.
19. Introduction of motion
Forces
Laws of motion
Gravity
Velocity
Acceleration
Editor's Notes
You can see good examples of this idea when you see video footage of astronauts . Have you ever noticed that their tools float? They can just place them in space and they stay in one place. There is no interfering force to cause this situation to change. The same is true when they throw objects for the camera. Those objects move in a straight line. If they threw something when doing a spacewalk, that object would continue moving in the same direction and with the same speed unless interfered with; for example, if a planet's gravity pulled on it (Note: This is a really really simple way of descibing a big idea. You will learn all the real details - and math - when you start taking more advanced classes in physics.).
Think about the time you sit in a chair. Your body exerts a force downward and that chair needs to exert an equal force upward or the chair will collapse.