Gravitational Force: When an object is pull downward from the earth. This pull is called gravitational force.

Features of Gravitational force:

* All masses attract each other.

* The greater the masses , the stronger the force.

* The closer the masses , the stronger the force.

Weight: Weight is another name for the earth gravitational force on an object. It is measured in newtons (N).

Gravitational Field Strength: Gravitational field strength is represented by the symbol (g).

Equation: Weight = mass x g

Where , g = 10 N/Kg.

Air Tracker: It is a device where air is flow in and escapes through the sides of the tracker ,

providing a friction less surface for the glider.

Light Gate: It measures the time of interruption of the interruptor , t using the smart timer.

Distance: It is the change of position of a body. Its si unit is mitres . it is a scalar quantity .

Displacement: It is a change of position of a body (in a particular direction). Its si unit is mitres. It is vector quantity.

Vector quantity: These are the quantities which have both magnitude and direction. Eg: force , acceleration , weight , etc.

Scalar quantity: These are the quantities which have magnitude only . eg: mass, time,speed,etc.

Quantity: These are the parameters of physics , which is internationally recognized to quantify things. Eg: luminosity,length,etc.

Velocity: It is the rate of change of displacement with time. Its si unit is mitre/second. It is vector quantity.

Acceleration: It is the rate of change of velocity with time. Its si unit is m/s2. It is a vector quantity.

Deceleration: It is the rate of change of velocity with time , opposite to the direction of motion. Its si unit is m/s2. It is a vector quantity.

􀀀 A graph represents a relationship between two quantities and shows the variation between them .

􀀀 A displacement /distance time graph represents the change of position of a body over time.

􀀀 A velocity/speed time graph represents a variation and change of speed or velocity of that body.

NOTE: 1

The gradient of a x-t graph gives us the velocity or speed of the body.

NOTE: 2

The gradient of a v-t graph represents the acceleration of that body.

NOTE: 3

The area under the v-t graph represents the displacement travel over time.

􀀀 A graph of acceleration versus time shows the variation or change of velocity of an object over time.

NOTE: 4

Area under the a-t graph represents the change in velocity of the body.

Gradient=change in y /change in x = y2-y1/x2-x1

Ticker timer take:

Ticker timer take: A ticker timer is a device which is used to measure and record distance , using a mitre rule and time , using dot spacing.

A ticker time make 50 dots in 1 second.

For 1 dot spacing = 1/50=0.02 second.

A ticker timer is used to record and observe the motion of a body.

NOTE:

Equal dot spacing represent constant velocity (acceleration=0).

Dot spacing = no. of dots in a length-1.

Example: V_ab=(80/100)/0.02~10 seconds.

Note:

When a body is moving by uniform acceleration , the average velocity is calculated by

Velocity average=u+v/2 (constant acceleration).

Air Resistance: It is the resistive force acting on a body , when it travels through air. Air resistance increases with the increase in velocity of travel of the body.

Terminal velocity: When an object falls through air , eg: an object free falling , sky drivers; It accelerates downwards. Initially the velocity is zero (downward) , and this velocity increases with acceleration.

*As a velocity increases , the air resistance increases and the downward resultant acceleration decreases. At one point of the travel , the weight becomes equal to the upthrust force and drag force , resulting is zero acceleration. Since a = zero , the velocity doesnot change and the body moves with the velocity gained , which is constant. This is constant velocity is called the terminal velocity.

Factors affecting breaking distance:

1) Condition of the road surface . (Dry or wet).

2) Tyre break condition.

Force: Force is anything which changes the state of a body from rest or uniform motion. Its SI unit is ‘N’. It is vector quantity . Formula is ‘F = MA’.

Friction & Breaking: Friction is anything that opposes motion. It has the same value as the breaking force.

Stopping Distance: It is the sum of thinking distance / reaction time distance and breaking distance