Download Chapter 12: Forces and Motion

Chapter 12: Forces and
Motion
Section 12.1
Forces
Forces
 A push or pull that acts on an object
 Can cause an object to start moving or it can change an
object’s acceleration
 Measured in Newtons (N)
 Force is a vector ~ shows direction and magnitude
 Net force is the overall force acting on an object after all
forces have been combined.
Balanced and Unbalanced Forces
 Balanced forces combine to form a net force of 0.
 There is no change in the object’s motion.
 Unbalanced forces combine to form a net force not
equal to 0.
 Unbalanced forces cause objects to accelerate.
Friction
 A force that opposes the motion of objects that touch
each other
 Friction happens at the surface of objects (where they
touch)
 4 main types of friction
Static Friction
 Acts on objects that are not moving
 Always acts in the direction that is opposite of an
applied force
 Keeps an object from being moved across a surface
 Stops acting on an object once the object is moving
Sliding Friction
 Acts on an object once the object is moving
 Goes against the direction in which the object is
moving as it slides on a surface
 Occurs when two objects rub together
 Less of a force than static friction
Rolling Friction
 Force that acts on rolling (round) objects
 Acts on the surface and at the point where the object is
touching something else (the ground for example)
 Allows the object to touch the ground and not slip
 Slows rolling objects down
Fluid Friction
 Force that opposes an object’s motion through a fluid
(liquid or gas)
 Force increases as the object’s speed through the fluid
increases
 When fluid friction acts on objects moving through the
air, it is called air resistance.
Gravity
 Downward force that acts between any two masses
 An attractive force ~ pulls objects together
 Acts over large distances (unlike friction)
Falling objects
 Forces acting on a falling object:
 Gravity (pulling downward)
 Air resistance (acts in opposition to gravity, reduces
acceleration)
 Terminal velocity is reached when the force of air
resistance equals the gravitational force.
 The object is no longer accelerating.
 V= a x t speed of a falling object
Projectile Motion
 The motion of a falling object (called the projectile) after it
has been given a forward velocity (example: throwing
something forward)
 Air resistance and gravity act on the object.
 Because of the forward velocity and the downward
gravitational force, the object will follow a curved path.