Untitled Document-3 PDF Physics Notes

LEC 6 Issaac newton unified physics and astronomy laws of motion universal ale of gravitation Derived: speed of sound shape of the earth tides planetary and commet motion → Definitions Speed - the rate of change of position. That is, seepdometer measu...

LEC 6 Issaac newton unified physics and astronomy laws of motion universal ale of gravitation Derived: speed of sound shape of the earth tides planetary and commet motion → Definitions Speed - the rate of change of position. That is, seepdometer measures. (eg; the car is travelling 60km per hr) Velocity - speed and direction (eg; the car is going due north at 60km/hr Acceleration - the rate of change of velocity (eg; the car, traveling in a straight line, changes speed from 0km/hr to 100km/hr in 9s. ) → Newtons first laws: an object in motion remains in motion unless acted upon by an outside force → Newtons second law: Acceleration is proportional to force and inversely proportional to mass A = F/m or F = mA more force mean more acceleration more mass means less acceleration → Newtons third law - for every force, there is always an equal and opposite reaction force Momentum: Mass times Velocity P = mV → if you add uo the momentum of everything in a closed system, you will find that no matter what happens, this momentum is conserved. Angular Momentum: mass times velocity times distance (w = mVr) → if you add up the angular momentum of everything in a closed system, you will find that no matter what happens, angular momentum is conserved Newtons universal law of gravitation there is force between any two objects in the universe the force is proportional to the product of the masses of each object the force is inversely proportional to the square of the distance the force depend on M1 times M2 if you double the mass of either object, you double the force if you half the mass of either object, you half the force the force depends on the distance between the centres of the 2 objects if you double the distance, you reduce the force by a factor of 2x2 =4 if you half the distance, you increase the force by a factor of 2x2=4 Freefall When the only force acting on an object is gravity, we say you are in free fall. LEC 7 Newtons universal law of gravitation there is force between any two objects in the universe the force is proportional to the product of the masses of each object the force is inversely proportional to the square of the distance the force depend on M1 times M2 if you double the mass of either object, you double the force if you half the mass of either object, you half the force the force depends on the distance between the centres of the 2 objects if you double the distance, you reduce the force by a factor of 2x2 =4 if you half the distance, you increase the force by a factor of 2x2=4 Freefall  why is the astronaut floating and not falling to to earth? because he is in orbit, like his spacecraft He is travelling at around 26,000 km/h – so the force required to make him go in a circle is the same as the force of gravity. When the only force acting on an object is gravity, we say you are in free fall. → Tides the varying gravitational force squeezes both the earth and the moon Of course this doesn’t happen right away. Rock (and the Earth’s mantel) don’t bend quickly. The earth is rotating too quickly for the rock and mantle to really respond much Imagine if the earth were completely covered in oceans... They would have time to flow... The oceans respond to the tidal forces from the moon. → Tidal Locking Friction with the rotating earth causes the tidal bulge to lag behind. ← This lag applies a force on the earth, causing it’s rotation to slow down. ← The rotation period was 14 hours when the earth formed. Now it is 24 hours The tidal force on the moon by the Earth is much larger than the tidal force of the moon on the Earth. So the moon has already stopped relative to the earth. It is Tidal Locked > the sun also causes tidal waves on earth - In a full moon or a new moon the tidal forces from the moon and the earth add - This is called spring tide - In a quarter moon, the tidal forces from the sun partially cancel the tidal forces from the moon - This is called a neap tide