Forces

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calculated in g/cm^3

density of water: 1g/cm^3

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

calculate mass of irregular object by putting in measuring cylinder containing water, subtract by weight before

calculate volume by subtracting with object and without object in water

forces can change the shape of an object by:

- length

- width

- height

W = 10M on earth

w = mg

weight is measured in newtons

Gravity: force acting on a mass in a gravitational field

Gravitational field: a place where a mass experiences a force

Weight: force of gravity on a mass

Mass: measure of how much matter an object has (number of molecules)

Extension = f/k

extension = load/spring constant

Hooke's Law When an elastic object - such as a spring - is stretched, the increased length is called its extension. The extension of an elastic object is directly proportional to the force applied to it:

F = k × e

F is the force in newtons, N

k is the 'spring constant' in newtons per metre, N/m

e is the extension in metres, m

This equation works as long as the elastic limit (the limit of proportionality) is not exceeded. If a spring is stretched too much, for example, it will not return to its original length when the load is removed.

The spring constant The spring constant k is different for different objects and materials. It is found by carrying out an experiment. For example, the unloaded length of a spring is measured. Different numbers of slotted masses are added to the spring and its new length measured each time. The extension is the new length minus the unloaded length.

if forces are equal (and opposite) object is either stationary or at constant velocity

friction

thrust

normal reaction force

drag

air resistance

weight

upthrust/lift

Load and Extension

f = kx

Density

d = m/v

acceleration

RF = ma

pressure

p = f/a

f = N

x = cm

k = N/cm

d = kg/m^3

divide by 1000 to get g/cm^3

m = kg or g

v = cm3 or m3

rf = N

m = kg

a = m/s2

p = Pa = n/m2

f = N

a = m/s2

Density

forces

extension

Balanced and unbalanced forces

pressure