Phys WA2

Force and pressure

Weight

To find weight

W = mg

On earth g=10

A gravitational field is a region in which a mass experiences a force due to gravitational attraction.

Weight is a vector quantity

SI unit is Newton (N)

Forces

A force is a push or a pull

SI unit is Newton (N)

Instrument used to measure is force meter, spring balance newton meter

Vector quantity incl. magnitude and direction

Meter → instrument → voltmeter

Metre → unit of length → metre rule

Volume

Volume is defined as the amount of space that matter takes up.

SI unit for volume is cubic metres (m^3)

Density

Density of a substance is defined as its mass per unit volume

SI unit for density is kilogram per cubic metre (kg/m^3)

ρ = m/v

g/kg^3 x1000 = kg/m^3

Pressure

P = f/a

The SI unit of pressure is the pascal (Pa)

Acceleration

The rate of change of velocity with time

SI Unit is metre per second per second (m/s^2)

Acceleration = Change in velocity/TIme taken

AKA a = v-u/t

Dynamics

Newton’s first law of motion

Every object continues in its state of rest or uniform motion in a straight line unless a resultant force acts on it to change its state

At any time, multiple forces may be acting on an object in different directions. We add them up to give a single vector called the resultant force

When the forces acting on an object is balanced (resultant force = 0 N), the object can either be at rest or moving at constant speed. (Acceleration = 0 m s^-2)

When the forces acting on an object is unbalanced (resultant force ≠ 0), the object is accelerating

Newton’s second law of motion

The resultant force acting on an object is equal to the product of the mass and the acceleration of the object.

F = ma

Newton’s third law of motion

For every force that is exerted by one body on another, there is an equal and opposite force exerted by the second body on the first.

These forces are called action and reaction forces

These forces are equal in magnitude, but opposite in direction

Friction and its effects

Friction is a contact force that slows down moving objects

Frictional forces exist even in objects that are at rest.

Friction is very important in our daily life and has both positive and negative effects.

Energy

Energy is required for things to work

SI unit for energy is joule (J)

Energy transfers

1. Energy transferred mechanically by a force acting over a distance

2. Energy transferred by heating due to a temp. diff.

3. (a) energy transferred by propagation of waves (electromagnetic waves)

   (b) energy transferred by propagation of waves (mechanical sound waves)

4. Energy transferred electrically by an electric circuit

Kinetic energy (KE)

kinetic energy is energy possessed by a body by virtue of its motion.

KE = 1/2 mv^2

Gravitational potential energy (GPE)

gravitational potential energy is the energy possessed by the body by virtue of its raised position.

GPE = mgh