Physics Notes On Force & Netwons’ Law

What is Force?

We define Force as:
1) Force is a push or pull. 

2) Force is the capacity to do work or cause physical change. 

3) Force= Mass times acceleration (F = ma)

4) A force is that which changes or tends to change the state of rest or
motion of a body. 





Let’s See Some Examples here
For simplicity sake, all forces (interactions) between objects can be
placed into two broad categories: contact forces, and forces resulting from
action-at-a-distance.
also,
Contact Forces include frictional forces, buoyant forces, normal forces,
and air resistance forces….
while,
Action-at-a-distance forces include gravitation, electrostatic and magnetic
forces.

Measurement of Force
Force is measured using either the English System of Measurements or the
International System of Units (SI).
the most Common Units of Force are as following;
—>>SI: Newton (N) 1 N = 0.225 lb; 
One Newton (N) of force is
defined as the amount of force needed to accede of mass at a rate of 1 meter per second squared (m/s^2).
1 Newton = 1 kg m/sec2 (A kilogram is the amount of weight at which 1 N of
force will accelerate at a rate of 1 m/s^2.) 
—>>English System: Pound (LB) 1 LB = 4.448 N
In English system of measurements, a slug is the amount of mass that 1
pound of force will accelerate at 1 ft/s^2, and a pound mass is the amount of
mass that 1 LB of force will accelerate at 32 feet/s^2.

 Description of a Force
A force is a vector quantity. A vector quantity is a quantity which has
both magnitude and direction. To fully describe the force acting upon an
object, you must describe both its magnitude and direction.
Thus we see, 10 Newtons of force is not a complete description of the force
acting on an object. 10 Newtons, downwards is a complete description of the
force acting upon an object.
  
Now we must learn What the
difference between vector and scalar quantities is?
A vector has both strength and
direction, a scalar quantity can be described using only 1 quantity, magnitude.
Example of vector quantities are
velocity, acceleration etc.
Examples of scalar quantities are
time, energy and volume since they only represent magnitude and no direction. 

What is the Difference between
Mass and Weight?
Shown below are two types of
scales commonly used in the classroom –a spring scale (left) and a simple
balance beam scale on the right.
On earth the spring scale reads
100g with an unknown mass attached at the bottom. To balance the scale on the
right a 100g mass was also needed.
 If we were to take both scales to the moon,
what would the the spring scale read? How much mass would be needed to balance
the 100g mass on the balance beam? 

What does applying a Force do?
Force causes acceleration
Newton’s Second Law states that:
the acceleration (a) of an object is directly proportional to the force (F)
applied, and inversely proportional the object’s mass (m).
That means that the more force
you apply to an object, the greater the acceleration. And, the more mass the
object has, the lower the acceleration.

Newton’s Second Law can be
written in equation form:
 F = ma.
For falling objects we can write
F=mg where g is the acceleration due to gravity. The force of gravity is what
causes free falling objects to accelerate. These objects all accelerate at the
same rate of 9.8 meters/sec^2.

What is Friction?
Friction is the force that
opposes the relative motion or tendency to such motion of two bodies in
contact. If we try to push a block of wood across a table, there are two
opposing forces that act: the force associated with the push, and a force that
is associated with the friction which acts in the opposite direction. As
frictional forces are decreased (for example, by placing oil on the table) the
object moves further and further before stopping. This demonstrates Galileo’s
law of inertia too.

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43 Comments

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