Transcript 1.0 Newtons laws

Forces
• Def – an action exerted on an object to change
the object’s state of motion (resting or moving)
– Magnitude and direction
– Units: Newtons (N)
• Net force – total force on an object
– When there is a net force on an object, the object
accelerates in the direction of the net force
– If net force = 0, then the object does not move
Balanced forces
• Net force = 0, no movement
– Forces are balanced
– An object standing still will not move
– An object moving will not stop
Unbalanced Forces
• Net force is greater than zero, unbalanced
force
– Object will move
Friction
• Force that opposes motion between two surfaces
that are in contact
2 types
– Static – friction between two forces at rest, initial
friction an object must overcome
– Kinetic – friction between two moving objects
• Static friction is usually greater
Newton’s Laws
• He was born the same
year that Galileo died
• Newton had ideas about
motion, which he called
his three laws of motion
– Also had ideas about
gravity, the diffraction of
light, and forces
• Physics and Math
• Helped create Calculus
First Law
• Law of inertia
– An object at rest will stay at rest and an object in
motion stays in motion unless acted on by an external
force
• Inertia – tendency of an object to stay at rest or
stay in motion
– Mass is a measure of inertia
– Small mass = less inertia
• Seatbelts
Second Law
• The unbalanced force acting on an object
equals the object’s mass times its acceleration
– F=ma
– Force is measured in Newtons (N)
• 1 N = 1 kg x 1 m/s2
Q: What is the force necessary for a 1600 kg car
to accelerate forward at 2.0 m/s2 ?
2nd Law Problem
Mike's car, which weighs 1,000 kg, is out of gas.
Mike is trying to push the car to a gas station,
and he makes the car go 0.05 m/s2 . Using
Newton's Second Law, compute how much
force Mike is applying to the car.
Third Law
• For every action there is an equal and opposite
reaction
– Opposite in direction.
– Whenever an object pushes another object it gets
pushed back in the opposite direction equally hard
• Example: Balloon full of air being released
Force of Gravity
• All objects in the universe attract each other
through gravitational force
• Mass increases – force of gravity increases
• Distance increases – force of gravity decreases
Force of Gravity
• Free fall – only force of gravity is affecting an
object
• Calculate the acceleration at which an object
free falls
– Earth – 9.8 m/s2
Force of Gravity
• Weight is not the same as mass
– Depends on gravity
– Different locations have different gravities and
therefore different weights
• Force of gravity on an object is weight
– w=mg
– Newtons (N)