Slide 1

L2 Forces, Mass, Acceleration, Pressure, Review of ExponentsFrictionless motionDemo5.NEWTONS FIRST LAW OF MOTIONNewton finished the overthrow of Aristotelian ideas.

Law 1 (Law of Inertia) Every object continues in its state of rest, or of uniform motion in a straight line, unless it is compelled to change that state by forces impressed upon it.If you leave an object alone, it has constant velocity. Newton's concept of motion said that the natural state of an object was(a)constant velocity(b)constant acceleration(c)constant net force

Inertial massWe call the change in velocity per unit time the accelerationa= v/ tThe v can be in magnitude and/or directionFORCE CAUSES ACCELERATION

The combination of forces that act on an object is the net force.(Only the net force is shown in the figures on this slide.)

FaFaFaThe acceleration of an object is directly proportional to the net force.mmmThis symbol means proportional to7The force in each of these equations represents the vector sum of all of the forces acting on the object of mass m.Units of force - N and lb

or5. NEWTONS SECOND LAW OF MOTION8 slug)A slug weighs Every object possesses inertia (mass).Inertia is the sluggishness of an object to changes in its state of motion.Mass - a measure of the inertia of an object(Units - kg and

3.MASS AND WEIGHT

32 lb.Inertia deals with how hard it is to start and stop an object.9Gravitational MassNewton's Law of Universal Gravitation

rm1m22.The Universal Gravitational Constant, G

At earths surface,F = G mMe/Re2 orW = (Gme/Re2) m or W=(g)m or

weight = mass x acceleration of gravity

g = 9.8 m/s2

A 2 kg mass weighs:A) 2 NB) 19.6 NC) 32 ND) 105 NE) Not enough information given

2 Concepts of Mass:

Equivalence of gravitational mass and Inertial mass

Theory of General relativity

Pressure=Force/contact area

On left, the pressure on the bottom block, i.e. the weight of the top block/contact area, is lower than the pressure on the bottom block on the right.

Pressure in a fluid (including air!)

Exponential Notation1000 = 10 x 10 x 10 = 103 100 = 10 x 10 = 102 10 = 101 1 = 100 0.1 = 1/10 = 10-10.01 = 1/100 = 10-2 0.001 = 1/1000 = 10-3 Ordinary decimal notationScientific notation (normalised)30031024,00041035,720,000,0005.721090.00000000616.1109For CAPA, we write356 as 3.56E210-2 x 10+6 = 104

10-2/106 = 10-8