Transcript Forces - Riverside High School

FORCES
Chapter 3
FORCE DIAGRAMS

Way of representing forces

Use arrows to represent amount

PhET simulation – Forces and Motion: Basics
TYPES OF FORCES

Contact
Anything touching an object is exerting a force on the object
Surfaces, hand, rope/cord, friction, etc

Non-contact
Any force that acts without touching
Gravitational force
NEWTON’S 3RD LAW


When a force is exerted by one object on another,
the other object simultaneously exerts a force on
the first object
Forces come in pairs called Interaction Pairs
Can you touch something without being touched?
Can something interact with you without you interacting with it?
FRICTION
Force
 Opposes the direction of motion
 Unbalanced force

AIR RESISTANCE

Force that is friction-like

Opposes the motion of object through air
o Objects fall at the same speed in a vacuum
o Depends on size and shape of object
o But NOT mass
NEWTON’S SECOND LAW OF MOTION

Exertion of greater force results in greater
velocity (and, therefore, acceleration)
Fnet = ma
Acceleration occurs in the direction of the net force
What about objects with different masses?
GRAVITY
Attractive non-contact force
 Depends on mass of object
 1 of 4 basic forces



Gravitational, weak nuclear, strong nuclear, EM
Described by Law of Universal Gravitation
GRAVITATIONAL ACCELERATION

Free fall


Object falling when gravity is the only force acting on
the object
Objects in free fall have the same acceleration
9.8 m/s2 on Earth
Called acceleration due to gravity
Identified as g
NEWTON’S 2ND REVISITED
Fnet = ma
Fweight = magravity
Fw = mg

Weight is a force

Weight is NOT the same as mass
WEIGHTLESSNESS AND FREE FALL

Weightlessness is experienced in space

Space shuttles are really in free fall
PROJECTILE MOTION

MythBusters clip
Newton’s 1st Law
An object in motion will stay in motion until an
unbalanced force acts on it
Gravity is the unbalanced force
SATELLITES



In projectile motion
around Earth
Being pulled to the
center by Earth’s
gravitational field
Moving forward because
of Newton’s 1st law
MOMENTUM
Property of a moving object
 Related to the amount of force required to change
the object’s motion

Momentum cannot be
lost or destroyed, but
it can be transferred