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