Download Lecture - Force and Acceleration File

SACE Stage 1 Conceptual
Physics
Newton’s Second Law of Motion –
Force and Acceleration
Force Causes Acceleration


Forces are what produce accelerations.
Acceleration is caused by forces.
F  ma
Force is proportional to acceleration.
Fa
Force Causes Acceleration

When objects
accelerate, it can be
caused by a number
of different forces.
This supplies a net
force on the object.

Applet – Net Force
Mass Resists Acceleration
Acceleration depends on
the mass being pushed
 Greater the mass, the
less the acceleration.
 Greater the acceleration,
smaller the mass.

Mass Resists Acceleration

For a given force, the acceleration produced is
inversely proportional to the mass.
1
acceleration 
mass
Mass Resists Acceleration
Newton’s Second Law

Definition – The acceleration produced by a net
force on an object is directly proportional to the
magnitude of the net force, is in the same
direction as the net force and is inversely
proportional to the mass of the body.
F
a
m
Newtons Second Law Experiment

Using the applet, determine the
acceleration of the block.
Statics

How many forces are acting on these
stationary objects!
Friction
Friction is caused largely due to the
irregularities in the 2 surfaces of the
objects.
 If viewed under a microscope, the even
the surface of a mirror will appear rough.

Friction

Friction always acts in the opposite
direction of the motion.
Friction - Questions

Suppose a high flying jet cruises at
constant velocity when the thrust of its
engines is a constant 80 000N. What is
the acceleration of the jet? What is the
force of air resistance acting on the jet?
Friction - Questions
Answer – The acceleration is zero because
the velocity is constant.
As the acceleration is zero, the net force
must be zero, therefore the thrust must
equal the amount of air resistance on the
jet, i.e., 80 000N in the opposite direction
of the velocity.
Applying Force - Pressure
Force
Pressure 
area of applicatio n
You can place a book on the table and no matter
what way you place it, the force will always be the
same. You can check this by using a bathroom
scale.
The book on the right is exerting more pressure on
the table than the book on the left.