 # Motion occurs when an object changes position.

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Motion occurs when an object changes position.
What is Motion? Motion is the study of how something moves. It is all around us even though we sometimes cannot see it! Motion occurs when an object changes position.

Motion Motion is relative
A book at rest relative to the table it lies on is moving at about 30 km/s relative to the sun. Motion is always described relative to something else.

Motion DISTANCE VERSUS DISPLACEMENT
Distance and displacement are not the same things. Displacement is the distance and direction of an object’s final position from its initial position. Distance does not involve direction.

Motion DISTANCE VERSUS DISPLACEMENT Displacement is a vector value.
A vector is a quantity that is specified by both a size and a direction.

Average speed = distance
Speed is the measure of how fast an object is moving Speed is usually expressed in meters/second or mph (miles per hour) Average speed can be calculated using this formula: Average speed = distance time

Speed Average Speed is different from instantaneous speed (speed at any second).

How is speed different from velocity?
Velocity: Velocity is speed WITH DIRECTION!!!!! The velocity of an object can change, even though the speed of the object remains constant.

HOW DO YOU MEASURE CHANGES
IN SPEED OR VELOCITY? ACCELERATION – Change in the speed or direction of an object over time. *A decrease in velocity is negative acceleration *An increase in velocity is positive acceleration

HOW DO YOU MEASURE CHANGES
IN SPEED OR VELOCITY? ACCELERATION = change in velocity time interval OR more precisely, ending velocity-initial velocity

Force Force is any push or pull that is exerted on an object, and is a vector value.

Force Causes Acceleration
Force causes acceleration – think of a hockey puck being hit again after it is already in motion. To increase the acceleration of an object, you must increase the net force acting on it!

Force Causes Acceleration
Net force is directly proportional to acceleration. F ~ a.

Force Causes Acceleration
Forces can be balanced or unbalanced. If forces are balanced, there is no net acceleration. Unbalanced forces result in an acceleration.

Applying Force – Pressure
Pressure is the amount of force per unit area. P = F / A It is measured in pascals (Pa). 1 Pa = 1 N/m2

Mass Resists Acceleration Acceleration also depends upon mass.
They are inversely proportional. a ~ 1/m.

Friction Friction always acts in a direction to oppose motion.
The force of friction between the surfaces depends on the kinds of material in contact and how much the surfaces are pressed together.

Friction There are three types of friction:
Static friction – The frictional force that prevents two surfaces in contact from sliding past each other

Friction 2) Sliding Friction – The force that acts in the opposite direction to the motion of a surface sliding on another surface.

Friction 3) Rolling Friction – Frictional force resisting motion in the direction of a force. Rolling friction is usually less than sliding friction.

Friction Air Resistance is a form of friction between objects and air molecules. The amount of air resistance on an object depends on the size, shape, and speed of the object.

Falling and Air Resistance
If the air resistance of a falling object reaches a point to where it equals the weight of the object, the net force will be zero and will no longer accelerate. This is called terminal velocity. THIS DOES NOT MEAN THAT THERE IS NO MOVEMENT!

Falling and Air Resistance
A skydiver reaches a terminal velocity of 150 – 200 km/h on average. At low speeds, air resistance is often negligible, but at high speeds, it can make a big difference.

Free Fall If there is no air resistance and gravity is the only thing affecting a falling object, it is in free fall. All falling objects accelerate due to gravity.

Free Fall The value for the acceleration due to gravity is g = 9.8 m/s2 (10 m/s2) For objects thrown upward, the speed decreases upward the same rate as the speed increases moving downward.

Free Fall To determine the distance an object falls during free fall use d = ½ gt2

Air Resistance and Falling Objects
With negligible air resistance, all falling objects can be considered to be falling freely.

Air Resistance and Falling Objects
The effects of air resistance are less noticeable with more compact objects.

Projectiles near the Earth always follow a curved path.
Projectile Motion A projectile is an object that has been shot or thrown through the air. Projectiles near the Earth always follow a curved path.

Projectile Motion They have both horizontal and vertical velocity, which is what results in the curve.

Upwardly Launched Projectiles Without gravity, a projectile fired upwards would follow a straight-line path. Monkey and zookeeper Link

Projectile Motion If air resistance is negligible, a projectile will rise to its maximum height in the same time it takes to fall from that height to the ground because of gravity.

Projectile Motion A ball thrown and a ball dropped from the same distance will both hit the ground at the same time – Why? Link

Projectile Motion

Projectile Motion With significant air resistance, the range of a projectile is diminished and the path is not a true parabola.

Universal Gravitation
Newton’s Law of Universal Gravitation Gravity is a property of matter. If an object has mass and takes up space, it has a gravitational attraction to other objects.

Universal Gravitation
Newton’s Law of Universal Gravitation Every object attracts every other object with a force that for any two objects is directly proportional to the mass of each object.

Universal Gravitation
Newton’s Law of Universal Gravitation The greater the masses, the greater the force of attraction between them.

Universal Gravitation
Newton’s Law of Universal Gravitation The farther away the objects are from each other, the less the force of attraction between them.

Universal Gravitation
Newton’s Law of Universal Gravitation F = G m1m2 d2 G = universal gravitational constant G = 6.67 x Nm2/kg2

Gravitation decreases according to the inverse-square law.
The force of gravity weakens as the distance squared. Ex: If you were three times farther from the center of the Earth as you are now, your weight would be 1/9 of what it is now.

Einstein’s Theory of Relativity
Einstein theorized that the mass of an object distorts space time. This was his explanation for gravitational influence.

Newton's Laws Newton’s First Law of Motion (Law of Inertia) – every object continues at rest, or in motion in a straight line at constant speed, unless acted upon by an outside force.

What is momentum? Momentum = an object’s mass x its velocity (speed with direction). SO, Momentum = mass x velocity OR p=mv A train has more momentum than a tennis ball? Why

Law of conservation of Momentum
We all have laws!! Even momentum! Law of conservation of Momentum The total amount of momentum in a system is conserved What does that mean????????????

Newton's 2nd Law Newton’s 2nd Law of Motion states that force equals mass times acceleration. F=ma

NEWTON’S 3RD LAW OF MOTION – ACTION & REACTION
Interacting things exert forces on each other.

Newton’s 3rd Law of Motion
Newton’s 3rd Law of Motion - When one object exerts a force on a second object, it will exert an equal and opposite force on the first object.

Newton’s 3rd Law of Motion
One force is called the action force and the other force is called the reaction force. Ex: letting air out of a balloon, bird flying through the air, walking, & space shuttle lifting off.

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