Forces
Unit for forces
Newtons N kg.m/s^2
MOMENTUM
Property of a moving object that equals its mass times its velocity
Types of Friction
Static Friction the frictional force between two surfaces that are not moving past one another. must be overcome by a force before motion can occur because micro welds are so strongly such together Sliding Friction the frictional force that opposes the motion of two surfaces sliding past each other easier than static because they don't have time to stick Rolling Friction the frictional forces between surfaces rolling past each other usually much less than sliding friction because they have no time to form micro welds
Inertia
THE TENDENCY OF AN OBJECT TO RESIST ANY CHANGE IN ITS MOTION The more mass an object has, the greater its inertia. Not a force
NEWTON
The amount of force that will give a one kilogram mass and acceleration of one m/ss
Without air resistance a rock and a feather take the same amount of time to hit the ground because
The greater the mass of an object, the greater its force of gravity. Unbalanced forces cause acceleration: a = f/m A large force & a large mass gives the same acceleration as a small force & a small mass When air resistance has a significant effect, more massive objects fall faster than less massive objects.
Newton's Second Law
The net force acting on an object causes the object to accelerate in the direction of the net force. The greater the mass (of the object being accelerated) the greater the amount of force needed (to accelerate the object). force = mass x acceleration
Law of Conservation of Momentum
The total momentum at the start of an action is the same as the total momentum at the end.
Terminal Velocity
This is the highest velocity that will be reached by a free falling object. Air resistance increases until it balances the pull of gravity. (Forces are now balanced. Net force = zero. No more acceleration) - Acceleration stops but the object continues to fall at a constant velocity. (Click on picture) at this velocity weight and air resistance are equal
Two types of motion in a projectile
Vertical motion - due to gravity pulling down Horizontal motion - parallel the earth's surface
Force
a force is a push or pull that one body exerts on another.
g
acceleration due to force of gravity at Earth's surface This is the acceleration with which all free falling objects fall to the earth, regardless of mass.
Centripetal Acceleration
acceleration towards the center of a curved or circular path
Air resistance
acts in a direction opposite to the motion of the object. affects anything that moves in the Earth's atmosphere. Air resistance can alter or slow down g pushes up while g pushes down
Projectile
anything shot or thrown - there is force behind it, it is not free falling
Net force
combination of all the forces acting on an object vector
Newton's Third Law
for every action force there is an equal and opposite reaction force.
Balanced forces
forces that are equal in size but opposite in direction. stationary or moving with constant velocity net force is zero
The only downward force acting on a free falling object is
gravity.
Weight
is the measure of the force of gravity on an object - it measures how hard the earth is pulling down on an object.
Factors that affect gravity
mass distance apart
Friction is caused by
microwelds, which are formed when microscopic dips and bumps on the surfaces of all objects touch and stick or weld to each other.
Transfer of momentum
p can be transferred from one object to another Example: when playing a game of pool the momentum of the cue stick is transferred to the ball making the ball shoot across the table.
Unbalanced forces
produce a net force cause acceleration
Momentum
property Momentum must include direction (It will be the same as the direction of the velocity) The greater the momentum, the harder it is to stop an object.
Factors that affect air resistance
speed size shape (Not mass)
Friction
the force that opposes motion between two surfaces that are touching each other
Force can change
the speed of an object the direction in which the object is moving the shape of an object
Centripetal Force
this is the force pulling towards the center of a curved or circular path Ex. when turning the corner in a car, centripetal force is created by the friction between the tires and the road's surface.
Factors that affect friction
type of surface force pressing surfaces together
Velocity at any instance depends on
vi, weight, & the distance the object has fallen.
WEIGHT
A measure of pull of gravity on an object's mass
FORCE
A push or a pull exerted on an object
Types of Force
Contact force Friction Gravity Air resistance Centripetal force Tension and compression Magnetism
Momentum is dependent on
Depends on mass and velocity Symbol for momentum = p Momentum = mass (kg) x velocity (m/s) p = mv
Why forces aren't balanced according to the Third Law
Even though the forces are equal they are not balanced - they don't cancel each other! Ex. when shooting a basketball, you exert a force on the ball and the ball exerts that same force on you. But the ball has a smaller mass than you so it accelerates forward - not you
Gravity
Gravity is a force that acts towards the center of the earth. all masses exert an attractive force on each other anything that has mass is attracted by the force of gravity gravity depends on the mass of the objects and the distance between them.
Newton's First Law
IF THE FORCES ON AN OBJECT ARE IN BALANCE, THE OBJECT'S SPEED AND DIRECTION OF MOTION WILL NOT CHANGE. This means that if an object is not moving, it will stay still. If it is moving, it will continue in a straight line at constant speed unless it is affected by an outside force
Conservation of momentum
Momentum does not change unless an outside force acts on it.
Law of Gravity
- all masses exert an attractive force on each other anything that has mass is attracted by the force of gravity gravity depends on the mass of the objects and the distance between them. (only Earth is large enough and close enough for us to feel its gravity)
If the object is not moving, it has a momentum of
0 kg.m/s