Forces & Shape

* 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).

Force: Force is anything which changes the state of a body (at rest or at uniform motion). It’s SI unit is “N” or Newton. It is a vector quantity.

1 Newton: When a body of mass 1Kg is accelerated through 1 m/s2, then 1 Newton force is applied on the body.

Gravitational acceleration: It is the acceleration of earth or every object on its surface towards its centre. It is denoted by ‘g’.

g = 9.81 or 10 m/s2.

Types of Force:

  • Gravitational Force
  • Nuclear Force
  • Magnetic Force
  • Electrostatic Force
  • Frictional Force
  • Air Resistance or Fluid drag
  • Upthrust Force

Frictional Force: Friction is anything that opposes motion. It’s SI unit is ‘N’ or Newton.

Note: The friction between two solid bodies is called normal (perpendicular) contact frictional Force.

Note: The Friction between solid-fluid or fluid-fluid is called Air Resistance.

Fluid: Fluid is anything that flows.

 

Factors affecting Normal Contact Frictional Force:

  • Surface area in contact.
  • Weight or Normal Contact Force.
  • Texture, roughness, or smoothness.

Factors affecting Air Resistance or drag:

  • Velocity of the object.
  • Radius or equivalent radius.

Ticker timer: 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.

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

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