Download Physics(newton)

Mr. Fox’s Science Class
The insanity moves on!
Newton’s balls anyone?
Sir Isaac Newton
The fig newton is not named after
him!
Was in a heated competition with
Robert Hooke over who was
better for England.
One of the best Scientists to date
Came up with Laws on Motion
and mechanics
The Nature of Force
 Force – a push or a pull.
 Unbalanced forces – cause an object to start
moving, stop moving, or change direction.
 Balanced forces – equal forces acting in
opposite directions on an object
 Net Force – overall force on an object after all
the forces are added together.
Unbalanced Forces
An unbalanced force acting on an object
will change the object’s motion.
Balanced Forces
Balanced Forces
acting on an
object will not
change the
object’s motion.
Newton’s First Law of Motion
 Inertia – the tendency of an object to resist change in
it’s motion.
 Newton’s first law states - An object at rest will stay at
rest, or an object in motion will stay in motion, unless
acted upon by another unbalanced force.
Mass vs. Inertia
 Amount of Inertia depends on the mass of the object.
 The more mass an object has, the more resistant to
change in motion the object is going to have.
Newton’s Second Law of Motion
 The net force on an object is equal to the product of its
acceleration and its mass.
 OR
 Force = Mass x Acceleration
 Units: kg x m/s/s or N (for newton)
Practice Problems
 What is the force on a 1000kg elevator accelerating at
2m/s/s?
 How much force is needed to accelerate a 55kg runner
at 15m/s/s?
Gravity
 Obviously the force that holds us to the Earth.
 9.80665 m/s/s is acceleration due to gravity.
 How much do you weigh in newtons?
 1lb. = 0.4536kg
Gravity Confusion
 If two objects of different masses, are dropped in a
vacuum they would hit the ground at the same time.
 If one object is dropped straight down, and another
shot forward they will still hit the ground at the same
time. ( I will prove this on Monday. )
 So why don’t a leaf and an acorn hit the ground at the
same time when they both drop at the same time?
Weight
 Remember weight is caused by gravity! Everything
has mass, but only objects that are being pulled by
gravity have weight. Weight = Mass x (Acc. Due to
gravity)
 How much would you weigh on the moon? (Gravity =
1.65m/s/s)
 How much would you weigh on Jupiter? (Gravity =
25.93 m/s/s)
Friction
 The force that one surface exerts on another when the
two rub against each other.
 The strength depends on the type of surface and how
hard the surfaces are pushed together.
 Is friction useful?
Types of Friction
 Sliding Friction – when solid surfaces slide over each
other.
 Rolling Friction – when an object rolls over a surface
 Fluid friction – friction that occurs when an object
moves through a fluid.
Air Resistance
 Objects falling through air experience fluid friction.
 The greater the surface area an object has the more air
resistance it encounters.
Newton’s
rd
3
Law of Motion
 If one object exerts a force on another object, then the
second object exerts a force of equal strength in the
opposite direction on the first object.
 For every reaction… there is an equal and opposite
reaction.
Momentum
 Explains why someone would want to catch a baseball
at 90mph rather than a car at 90mph.
 Momentum = Mass x Velocity
 kg · m/s
 No fancy unit name.
 Think of momentum as damage!
Practice
 1. If a car with a mass of 500kg has an acceleration of
120m/s/s. How much force is acting upon the car?
 2. Mr. Fox is exerting a force of 3135N. We know he has
a mass of 122kg. How much is he accelerating?
 3. An unknown object has a mass of 0.14kg and a
velocity of 42.4688m/s. Another unknown has a mass
of 0.042kg and a velocity of 935m/s. Which has more
momentum? Which one would cause more damage?
What do you think the two objects are?