A100 Movie Special Tuesday, March 23 Swain West 119 7:00 pm (153 minutes) Winner of several awards 20 activity points! BYOP (Bring Your Own Popcorn)

Matter, Forces and Motion

Scalars and Vectors Scalar: a quantity described solely by its size (and units) Vector: a quantity described by its size AND direction

speed – rate at which an object moves [e.g., m/s]. A scalar quantity. velocity – an object’s speed AND direction, [e.g.,10 m/s east]. A vector quantity. acceleration – a change in an object’s velocity, i.e., a change in speed OR direction [m/s 2 ]. A vector quantity.

Momentum (p) – the mass of an object times its velocity (p=mv) Force (f) – anything that can cause a change in an object’s momentum As long as the object’s mass does not change, a force causes a change in velocity, or an acceleration (a) Force, momentum, and acceleration are all vectors

What is the natural state of motion?

Newton’s First Law of Motion A body in motion remains in motion and a body at rest remains at rest unless acted upon by an outside force. If the net force acting on an object is zero, then there is no change in the object’s motion. OR

What happens when there are forces?

The change in a body’s velocity due to an applied force is in the same direction as the force, and is proportional to the force, but is inversely proportional to the body’s mass. F = ma Or F = rate of change of momentum Newton’s Second Law of Motion

Because force is a vector, forces only affect motion in the direction of the force. Motion perpendicular to the force is unchanged.

F = ma can be rewritten to show that for a given force, the acceleration is inversely proportional to the mass: a = F / m

Do not confuse mass and density Mass = amount of matter Density = amount of matter per volume Higher density means more matter packed into same volume

Momentum: p = mv Both p and v are vector quantities

Law of Conservation of Momentum If the net force acting on an object is zero, then the total momentum of a system remains constant.

Newton’s Third Law of Motion “For every applied force, a force of equal size but opposite direction arises” or For every action there is an equal and opposite reaction

A body in motion remains in motion and a body a rest remains at rest unless acted upon by an outside force. F = ma (= rate of change of momentum) For every applied force, a force of equal size but opposite direction arises. Newton's Laws of Motion

Conservation of energy Conservation of momentum Conservation of angular momentum Major Conservation Laws

Angular Momentum angular momentum – the momentum involved in spinning /circling = mass x velocity x radius ● torque – anything that can cause a change in an object’s angular momentum (twisting force)

Conservation of Angular Momentum In the absence of a net torque, the total angular momentum of a system remains constant.

Forces change momentum Torques change angular momentum

A planet is always changing its direction of motion. Newton’s second law therefore states that a force must be acting on the planet. Gravity provides this force. Gravity & Orbits

The angular momentum of an orbiting planet is conserved, i.e., it is always the same. This provides yet another reason why planets move fastest at perihelion and slowest at aphelion. Angular Momentum & Orbits

The Acceleration of Gravity (a force) As objects fall, they accelerate (a = g = F grav /m). We use the special symbol g to represent the acceleration due to the force of gravity. At sea level on the Earth, g = 9.8 m/s each second, or g = 9.8 m/s 2. The higher you drop the ball, the greater its velocity will be at impact (force will be acting on it longer).

Weight is the force of gravity acting upon an object : W = F g = mg

Galileo demonstrated that g is the same for all objects, regardless of their mass!

Is Mass the Same Thing as Weight? ● mass – the amount of matter in an object ● weight – a measurement of the force due to gravity acting upon an object When in free-fall, you still have weight! “weightless” is a misnomer W = mg (weight) F = ma

● Objects do have weight in space ● Free-fall often confused with weightlessness

Tidal Forces Because the gravitational force decreases with (distance) 2, the attractive force experienced by one object (e.g., the Earth) due to the gravitational field of a second object (e.g., the Moon) varies with position (closest parts attracted most strongly).

● Now look at what happens when we measure the forces relative to the center of the Earth.

Tidal Friction

● This fight between Moon’s pull & Earth’s rotation causes friction. ● Earth’s rotation slows down (1 sec every 50,000 yrs.) ● Conservation of angular momentum causes the Moon to move farther away from Earth.

Synchronous Rotation ● …is when the rotation period of a moon, planet, or star equals its orbital period about another object. ● Tidal friction on the Moon (caused by Earth) has slowed its rotation down to a period of one month. ● The Moon now rotates synchronously. – We always see the same side of the Moon. ● Tidal friction on the Moon has ceased since its tidal bulges are always aligned with Earth.

● Most of the large moons in the solar system are in synchronous rotation.