Physics Lecture 2

Front 1

What are Scalar Quantities?

Back 1

Scalar quantities have magnitude but no direction.

Front 2

Some examples of Scalar Quantities?

Back 2

Examples of Scalar Quantities
mass, time ,speed, distance, volume etc

Front 3

What are Vector Quantities?

Back 3

Vector quantities have both magnitude and direction.

Front 4

Some examples of Vector Quantities?

Back 4

Examples of Vector Quantities
displacement, velocity, acceleration

Front 5

What is Distance?

Back 5

Distance is concerned with how much ground is covered regardless of direction. Speed is the rate of change of distance

Front 6

What is Displacement?

Back 6

Displacement is distance in a specific direction or the change in position of an object.

Front 7

What is Velocity?

Back 7

Velocity is the rate of change of displacement.

Front 8

What is Acceleration?

Back 8

Acceleration is the rate of change of velocity.

Front 9

Formula for Average Speed?
Formula for Average Velocity?

Back 9

Average speed = total distance travelled/
total time taken

Average velocity = change in total displacement/
total time taken for change

Acceleration = change of velocity/
time

The instantaneous speed is the speed at any instant

Instantaneous velocity is the velocity at any given instant.

Front 10

Symbols used in equations of motion.

Back 10

Let the initial velocity of an object be u ms-1
Let the final velocity of an object be v ms-1
Let acceleration (assumed uniform) be a ms-2
Let the interval for the motion be t s
Let the displacement of the object be s m

Front 11

Acceleration=

Back 11

Acceleration(a) = change of velocity (v-u)/
time(t)

OR

v=u+at

Front 12

Displacement=

Back 12

Displacement = average velocity x time

Front 13

An object accelerates uniformly from 10ms-1 to 30ms-1 in 5s. What is:
a)The acceleration of the object?
b)The distance covered in the 5s?

Back 13

A) 30-10/5=4
B) Distance = Rate x Time
4 x 5 = 20 meter

Front 14

A car is travelling at 60ms-1 when the traffic light turns red. The car decelerates at 6ms-2 .
a)How long does the car take to stop.
b)How far from the lights must the driver start braking in order to not overshoot the lights.

Back 14

A) t= u-v/a
60-0/6=10s
B) x= (u+v)t/2
((60-0)/2) x 10

Front 15

What is a Projectile Motion?

Back 15

A projectile is an object which ,given an initial velocity continues in motion by its own inertia and is influenced only by the downward force of gravity.

Case 1: no gravity
The object will continue to move with the same speed and in the same direction

Case 2: gravity
The object will continue to move to horizontally while falling under gravity. There is no force in the horizontal direction so there is no acceleration in that direction. Producing a parabola

When an object is going up gravity is acting negatively it slows the object down.

When the object is going down gravity acts positively it speeds the object up.

Gravity has no impact on the horizontal component of velocity of the object it remains constant.

Front 16

Newtons first law?

Back 16

An object at rest remains at rest and an object in motion remains in motion until acted upon by an unbalanced force.

Front 17

Newtons second law?

Back 17

Force is equal to the rate of change of momentum.

F=ma

F= m(v-u)/t

Front 18

Newtons third law?

Back 18

For every action there is an equal and opposite reaction.

Front 19

A constant force changes the velocity of a 100kg sprinter from 4.0ms-1 to 6ms-1 in 1.0s. Calculate
a.The acceleration of the sprinter during this time.
b.The magnitude of the force

Back 19

A) Acceleration = v-u/t
6-4/1 = 2
B) F=ma
100KG x 2ms-1 = 200

Front 20

Linear momentum

Back 20

Linear momentum of an object (p) is the product of its mass and its velocity. Its units are kgms-1 .

Momentum is a vector quantity.

Front 21

Impulse?

Back 21

Impulse is equal to Force x time

Fxt= mΔv

this is called the impulse-momentum equation

Front 22

The principle of conservation of linear momentum states?

Back 22

The principle of conservation of linear momentum states that the total linear momentum of a system remains constant during collisions.

Front 23

In a head on collision between x and y which would have the positive and negative velocity?

Back 23

In the head on collision between x and y we assign objects moving to the right with a positive velocity and an object moving to the left with a negative velocity.
mxvx –myvy = -mxv`x + myv`y

Front 24

What is an elastic collision?

Back 24

Elastic : momentum is conserved, kinetic energy is conserved and total energy is conserved.

Particles approach at a given speed and after collision they recede with the velocity vector having the same magnitude but different sign.

Front 25

What is an elastic collision?

Back 25

Inelastic collisions: momentum conserved ,kinetic energy not conserved and total energy is conserved.

Front 26

What is work?

Back 26

An object which has the ability to do work is said to have energy.

Work is done when a force acts upon an object and displaces it .

The unit for work and energy is the JOULE J.

Front 27

Work=

Back 27

W= F x dCos θ F is the applied force
d is the displacement
θ is the angle between the force and displacement vectors

Front 28

Work again?

Back 28

When force and displacement are in the same directions
θ = 0
Cos θ = 1
W =Fxd

Front 29

What is energy?

Back 29

The energy acquired by objects on which work is done is known as mechanical energy. This energy is possessed due to Its stored energy (potential energy) Its motion(kinetic energy)

Front 30

Gravitational potential energy?

Back 30

Gravitational potential energy Energy that an object has because of its height above some reference point usually ground

Front 31

Elastic potential energy?

Back 31

Elastic potential energy Energy stored in some compresses or stretched elastic materials eg. wound up clock, compressed spring.

The amount of potential energy stored is related to the extent of the deformation of the material.

Front 32

Chemical potential energy?

Back 32

Chemical potential energy Energy stored in chemical compounds eg bonds in gasoline molecules

Front 33

Gravitational potential energy formula?

Back 33

Ep =mass (kg)x acceleration due to gravity(Nkg-1) x height(m)
Ep = mgh
45

Front 34

What is Kinetic Energy?

Back 34

Kinetic energy
This is the energy an object has because it is moving.

Kinetic energy (J) = ½ x mass x velocity2

Front 35

Difference between potential and kinetic energy?

Back 35

When an object is above ground the potential energy is maximum and kinetic energy is zero. Opposite for kinetic energy

At the instant before the object strikes the ground all its potential energy has been changed to kinetic energy.

Front 36

What is power?

Back 36

Power is the work done or energy converted per unit time.

Front 37

Power Formula?

Back 37

Power = force x displacement/time taken = Workdone/ time taken

Front 38

What is power measured in?

Back 38

Power is measured in Watts(W)