phyiscs exam one stuff

physica

normal force

Force with which a surface pushes back on an object, at right angles to the surface

Can’t use v= s/t when acceleration is not 0!!!



so cant use v=s/t when calculating vertical velocity coz accelrating due to gravity

when cant used v=s/t

\: Force which opposes the motion of the object through the air

Air resistance

effects of air resistance on projectile motion

1\.     Reduce its calculated range



2\.     Reduce its calculated maximum height



3\.     Increase its angle of descent

\-         Instantaneous velocity is tangential to circle



\-         Speed does not change, but velocity changes because it is constantly changing directions



\-         Therefore, there is acceleration towards centre



\-         Acceleration towards center is called centripetal force



\-         Centripetal force does not exist on its own, it is a RESULTANT force

reasoning for centripetal force

\-         On a banked track, the normal force is at an angle to the ground



\-         In then has vertical and horizontal components



\-         The vertical component balances gravity



\-         The horizontal component becomes the centripetal force



This force makes it possible to turn bend without friction due to a banked track. But there is an design speed to make this possible

circular motion on a banked track

\-         Velocity of object is tangential to circular path which is horizontal at peak of loop



è Inertia wants object to keep going that way, yet tension force keeps in going in circular path



\-         Acceleration required for cicular motion is greater than 9.8m/s/sà object velocity is faster than gravity would normally cause



\-         The structure holding the object (e.g bucket holding water) pushes into the object as it falls, so the object stays in contact with the structure

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Why Stuff doesn’t fall down when at top:

if centripetal acceleration is greater than 9.8m/s

at what velociuty will objets stick to top of circular motion

FN= 0

Min velocity to keep in contact is

Gravity force is greater than normal force

On a bump….

Normal force is greater than gravity force

in a ditch …

a measurement of the amount of force applied to an object to make it rotate around an axis.

Torque

state of balance when the net force acting on an object is equal to zero

Equilibrium:

average position of all the particles in an object

Centre of mass:

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\-         The vertical line through the centre of gravity (CG) falls through the base. Hence, the object will return to the equilibrium position

1\.     Stable Equilibrium

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\-         The vertica line through the CG does not go through the base. Hence, the object does not return to its equilibrium position. Instead, it topples over ( object will fall on side the centre of gravity goes through)

1\.     Unstable Equilibrium

\-         With circular objects



\-         The vertical line through the CG always goes through the edge, there in no specific base and no pivot. If a face is applied the object may roll on its surface but will not roll over

1\.     Neutral Equilibrium

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\-         Lower centre of gravity



o    Larger mass on bottom



o   Make object shorter



\-         Larger base

how to increase stability

Normal force> weight



Fnet= FN – Fg



 Ma=FN – mg

when accelerating upwards…..

   Weight > normal Force



   Fnet= Fg – FN



   Ma= mg- FN

when accelerating downwards…

\-         The force due to gravity between two masses is directly proportional to the product of the masses and inversely proportional to the square of distance between the masses

Newton’s universal law of gravitation:

  Area under force distance graph= change in energy or work done

How to calculate the change in energy from a force-distance graph

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\-         Moon, falls infinitely towards Earth with a velocity and radius that allows it to come back to its original point and not land



\-         The force causing circular motion, Fc is the force due to gravity

how moon stays above earth

# Kepler’s Laws:



1\.     Satleiites have elliptical orbits around earth



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2\.     The area swept by the moon when it is orbiting the earth is the same for the same time



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3\.     Relationship between time period and radius of r3 to T2 is a constant

keplers’s laws

Satleiites have elliptical orbits around earth

kepler’s first law

2\.     The area swept by the moon when it is orbiting the earth is the same for the same time

kepplers second law

3\.     Relationship between time period and radius of r3 to T2 is a constant

kepplers third law

\-         Stationary relevant to Earth



\-         Satleiite stays above the same spot for the time



\-         Over the equator



\-         Type of geosynchronous satellite



\-         R=36000km



\-         T=sidereal day= approximately 24 hours

geostationary

\-         In synch with Earth rotation



\-         Doesn’t have to be placed above equator



\-         Can be inclined



\-         R= approx. 24 hours



\-         R=36000 km



 

geosynchronous