Physics - Newton's Law of Motions and Kepler Laws

Sir Isaac Newton

the originator of the laws of motion.

Force

• an external cause or influence that can change the position, speed, and state of an object.

• a push or pull

• measure in the SI unit of newton (N)

• represented by the symbol F

Inertia

the tendency of an object to resist changes in its velocity: whether in motion or motionless.

Law of Inertia (first law)

• Objects in motion will stay in motion, and objects at rest will stay at rest– unless acted upon by an unbalanced force.

• ex. The gold ball will remain on the ground until the golfer hits it.

• The soccer ball will remain on the ground until the player kicks it.

• Imagine that you are standing still in a stationary train, and then suddenly it moves forward.

• • Your body has inertia, and so a force is needed to change its velocity.

• • The train floor accelerates your feet but your body falls backward.

• • As you hold on to the handle, the force exerted by the train through the handle gives your body forward velocity.

Law of Acceleration (2nd law)

• States that the acceleration of an object with constant mass is proportional to the net force action on it and is in the same direction as the net force.

• When an UNBALANCED force is applied to a MASS, it causes it to ACCELERATE. Force equals mass times acceleration.

• ex. The car accelerates forward since the force due to its engine is greater than the friction of the road.

• Pushing an empty shopping cart is easier than pushing a loaded shopping cart. Because of the relation between the measles of the object, the force applied to it, and the acceleration produced.

• F = ma.

True

The greater the force that is applied, the GREATER the acceleration

False

The lesser the force that is applied, the greater the acceleration

Law of Interaction (3rd law)

• Action and Reaction

• Every action force has a reaction force that is equal in size and opposite in direction ( For every action there is an equal and opposite reaction )

Kepler's first law (law of ellipses)

• All planets revolve around the Sun in elliptical orbit with sun at one of the foci

• The planet to Sun distance is constantly changing

Kepler's Second law (law of equal areas / speed)

• The radius vector from the sun to the planet sweeps out equal parts of an area in equal times 

• The planet is moving fastest when it is at perihelion and slowest at aphelion.

Kepler's Third law ( law of harmonies)

• The square of the time period of revolution of a planet around the sun in an elliptical orbit is directly proportional to the cube of its semi-major axis.

• could also be T^2 = R^3

• T = orbital period

• d = distance in astronomical unit

1 au

1.5 x 10^8 km

Friction

• a force that happens when two surfaces rub against each other. It's like a sticky force that can make things harder to move smoothly.

Static Friction

• happens when an object is not moving and is touching a surface. This friction keeps the object from sliding or moving on the surface it's resting on.

Kinetic Friction

• The force that opposes the motion of an object sliding or moving across a surface.

Universal law of Gravitational

particle attracts every other particle in the universe