Unit types Physical Quantities – is one that can be measured or calculated and expressed in numbers
Scalar Quantities Scalar Quantities – is one with magnitude bit has no direction. (Think of a length of string, it has length but it has no direction) Examples of Scalar Quantities – length, mass, time, electric current, area, density, energy, electric charge/current, power and temperature
Vector Quantities Vector Quantities – one which has both magnitude and direction. (Think of acceleration of a car, it has magnitude but it has direction) Examples of Vector quantities – displacement, velocity, acceleration, force and momentum
Displacement Displacement – (s) is distance in a given direction. This is a vector quantity with a SI unit of meter (m). Think of your commute to school. Do you commute in a straight line from your home to school? Most of us must travel around roads that lead off track. Displacement is a straight line from point A to point B.
Velocity Velocity – (v or u) is the rate of displacement with respect to time. This is a vector quantity with SI unit of meter per second (ms-1). This is the speed in which an object can get from A to B in a straight in relation to time. Velocity = displacement time Average Velocity = initial velocity + final velocity time
Acceleration Acceleration – (a) is the rate of change of velocity with respect to time This is a vector quantity with an SI unit of meter per second squared (ms-2). Think of a fast sports car, when it starts of it does not immediately reach its maximum speed. It must climb or accelerate to this speed.
v = u + at s = ut + ½at² v² = u² + 2 ad u is the initial velocity, v is the final velocity, a is the acceleration,d is the ‘distance’ travelled, t is the time
Question 1 A body has an initial velocity of 8 ms-1 due west. Find its velocity after one minute if its acceleration is 1.5ms-2 W. 8
Question 2 A body has an initial velocity of 12.2 ms-1. Find its velocity after 3 minutes if its acceleration is 1.25 ms-2 W. 9
Question 3 A body accelerates from rest at a rate of 2.2 ms-2 for 9 seconds. Find(i) the initial velocity velocity of the body(ii) the distance travelled by the body after 9seconds. 10
Question 4 A runner accelerates from rest at the beginning of a race at a rate of 1.8 ms-2 for 5 seconds. Find (i) the initial velocity (ii) the final velocity after 5 seconds (iii) the distance ran in the time given. 11
Question 5 A body moves from rest for 4 seconds at an acceleration 6.4 ms-2. If its velocity remains constant for the next 8 seconds, and the body comes to rest after a further 10 seconds. Find(i) the initial velocity after the initial 4seconds.(ii) the distance travelled after the initial 4seconds 12
Question 6 A body begins to move from rest for 4 seconds, at an acceleration of 5ms-2. Its velocity remains constant for the next 8 seconds, and comes to rest after a further 7 seconds. Find(i) the velocity after the initial 4 seconds(ii) the distance after the initial 4 seconds.(iii) the distance travelled after thesubsequent 8 seconds(iv) the total distance travelled by the body. 13
Gravity Gravity: The force of attraction between any two bodies is directly proportional to the product of their masses, and inversely proportional to the square of the distance between them. Acceleration due to Gravity , ( g ) (i) Acceleration due to gravity , (g) means that free-falling bodies experience an acceleration towards the centre of the earth. g = 9.8 ms– 2 ( for all bodies, irrespective of their mass).
Gravity N.B.!!!! (a) If a body is moving from rest, its initial velocity is zero. (b) If a body falls vertically, its initial velocity is zero, and its acceleration is the acceleration due to gravity, g. => g = 9.8 ms– 2 . (c) If a body is travelling vertically upwards, its acceleration is – 9.8 ms– 2. (d) In calculations, use a formula with only one unknown.