Transcript Units for Force

Force
A little History
Isaac Newton was an English physicist/astronomer among
other things and made a number of significant advances in
the study of the world around us and in space.
He was allegedly struck on the head by
an apple falling from a tree which
eventually led to his developing his
three laws of motion now known as:
Newton’s Laws of Motion
Newton’s First Law
Newton’s First Law of Motion deals with the effects of
balanced and unbalanced forces. (Newton’s Law’s are one
of the main reasons that the units for force are in Newtons)
Wording of Newton’s First Law:
An object in motion will stay in motion
and an object at rest will stay at rest
unless an unbalanced force is acted
upon it
-- often called the law of inertia
Inertia
Inertia is the tendency of objects to resist any change in
motion.
The amount of inertia that an object has is directly related
to its mass
- the more massive an object is, the more inertia
an object has
Inertia
Think about it like this:
Which is harder to get rolling, a train or a Tonka
truck?
OR
Which would you rather try to stop, a train moving
at 5 km/hr or a Tonka truck moving at 5 km/hr?
More Examples Of Inertia
Example 1:
When you’re riding in a car, and the car slams on its
brakes, your body keeps going forward until a force acts
upon it. Hopefully, that force is the seat belt.
Example 2:
Demonstrations in the lab today with coins. Even
though the other coins/index cards moved, the coin stayed
still because no force was acted upon it
Newton’s First Law
Basically, an object will move at constant velocity
unless an unbalanced force is acted upon it
**remember that being stopped (a velocity of 0 m/s)
is still a constant velocity!!!**
What is this Force thing?
Force – the push or pull of one object on another
Force is a vector quantity, therefore, whenever calculating
force, you must give:
-- an amount
-- a unit
-- a direction
We very often represent the direction of force with arrows.
A glimpse of things to come…
Force is a measure of how strong the push or pull is on one
object by another.
Think about if you were pushing on objects in the real world.
If you push with all your might against a small box full of
feathers, you would get it moving faster than if you pushed
with all your might against a small box full of bricks.
Mass, as you will see, is a factor to consider when we talk
about forces.
Units for Force
Therefore, while mass is obviously a factor, speed and
acceleration also play a role in calculating force
When reporting force, we use the units of Newtons (N)
1 N = 1 kg m/s2
-- the units for Newtons are derived from the formula
for force, which we will look at later
-- YOU MUST ALWAYS remember that mass must
be in kilograms (kg) when calculating force
The unit Newton, of course, is named for the famous
scientist Sir Isaac Newton, who spent much of his time
investigating forces
Types of Forces
There are many different types of forces, including:
-- Frictional force (how strong friction is)
-- Gravitational force (weight)
-- Torque (perpendicular force)
No matter what type of force you are talking about acting
on an object, that force is either balanced or unbalanced
Questions
1. According to Newton, what do objects want to do?
Maintain their motion; stationary
Answer objects will continue to
not move and objects in motion will keep their same
velocity until acted upon by a net force
2. Which has more inertia, a walking elephant or an
eighth grader flying down Broad Street on a bike?
The elephant has more inertia
Answer
because it has more
mass. The velocity of an object does not affect its inertia
Questions
3. What is a force?
A force is any push or pull
Answer
one object exerts on another
4. What is the unit for force and where does it come
from?
The unit is the NewtonAnswer
(N) and it is made up of
kilograms times meters per second squared