Transcript Science in motion

NEWTON’S LAWS OF MOTION


A force is a push or a pull that can
cause acceleration to happen in an
object
We measure forces with the unit know
as a NEWTON (which is the force
needed to cause a 1 kilogram object ti
accelerate at 1m/s2)
A
frame of reference is the
perspective from which a system
is observed.
 Whenever you describe something
as moving you are comparing it to
a frame of reference that is
assumed to be stationary.
 There are NO truly STATIONARY
objects in the universe
- The Nature of Force
The
combination of all forces acting on an
object is called the net force.
- The Nature of Force
Unbalanced
forces acting on an object result in
a net force and cause a change in the object’s
motion.
- The Nature of Force
Balanced
forces acting on an object do not
change the object’s motion.
 “Things
keep
on moving the
way they are
moving" (unless
acted upon by
an unbalanced
force).
 Law
of Inertia: A
body remains at
rest or moving in a
straight line unless
acted upon by
some unbalanced
force
1. Imagine a place in the
cosmos far from all
gravitational and
frictional influences.
Suppose that an
astronaut in that place
throws a rock.
a The rock will
gradually stop.
b. continue in motion in
the same direction at
constant speed.

Mr. Wegley spends
most Sunday
afternoons at rest on
the sofa, watching
pro football games
and consuming large
quantities of food.
What effect (if any)
does this practice
have upon his
inertia? Explain.

Ben Tooclose is being chased through
the woods by a bull moose which he was
attempting to photograph. The enormous
mass of the bull moose is extremely
intimidating. Yet, if Ben makes a zigzag
pattern through the woods, he will be
able to use the large mass of the moose
to his own advantage. Explain this in
terms of inertia and Newton's first law of
motion.


F = ma : A force F
applied to a body with
mass m will cause it to
accelerate (change
speed and/or direction)
at rate a.
Or the harder the push
or pull the greater the
acceleration
 Force
= Mass x Acceleration
 Force is measured in units called
Newtons (N)
 A Newton (N) is = to the force
needed to make a 1Kilogram object
accelerate at 1
meter/second/second
 N=Kg
m/s2



In elephant-feather
scenario, we can say that the
elephant experiences a
much greater force (which
tends to produce large
accelerations. Yet, the mass
of an object resists
acceleration.
Thus, the greater mass of
the elephant (which tends to
produce small accelerations)
offsets the influence of the
greater force
It is the force/mass ratio
which determines the
acceleration

Action and Reaction:
Every force (or action)
applied, creates a
second equal but
opposite force (or
action) back on the
first body.

This law is
demonstrated by what
happens if we step off a
boat onto the bank of a
lake: as we move in the
direction of the shore,
the boat tends to move
in the opposite direction
(leaving us facedown in
the water, if we aren't
careful!).
- Friction and Gravity
Two
factors affect the gravitational attraction
between objects: mass and distance.
- Friction and Gravity
The
force of gravity on a person or object at
the surface of a planet is known as weight.
- Friction and Gravity
Use
the graph to
answer the following
questions.
- Friction and Gravity
Interpreting
Graphs:
◦What variable is on the
horizontal axis? The
vertical axis?
◦Time is on the
horizontal axis, and
speed is on the vertical
axis.
- Friction and Gravity
Calculating:
◦Calculate the slope of
the graph. What does the
slope tell you about the
object’s motion?
◦The slope is 9.8. The
speed increases by 9.8
m/s each second.
- Friction and Gravity
Predicting:
◦What will the speed of
the object be at 6
seconds?
◦58.8 m/s
- Friction and Gravity
Drawing
Conclusions:
◦Suppose another object
of the same size but with
a greater mass was
dropped instead. How
would the speed values
change?
◦The speed values would
not change.
- Friction and Gravity
Falling
objects with a greater surface area
experience more air resistance.
G=6.67x10^-11N
R=2GM/speed of light
squared

If I have seen further than other men, it is by
standing on the shoulders of giants.
◦
◦ Isaac Newton, Letter to Robert Hooke, February 5,
1675


I do not know what I may appear
to the world; but to myself I
seem to have been only like a boy
playing on the seashore, and
diverting myself, now and then
in finding a smoother pebble or a
prettier shell than ordinary,
whilst the great ocean of truth
lay all undiscovered before me.
Sir Issac Newton–(1643-1727)
 (1)
Speed=Distance/time
 (2)
Distance = Speed x time
 (3)
Time = distance/speed
 (4)
Accel = (Vf –Vi)/time
 If
Force=Mass x acceleration
 (5) F=ma
 Then
 (6) F/m=acceleration
 And
 (7)F/a=mass