Motion

•Position = location•Motion = Event that involves a change in the position or location of something •Distance is the total length traveled from motion…distance traveled depends on the path you take•Displacement is a straight line distance between 2 points•Reference point is a location to which you compare other locations•Change in position tells us that motion took place but doesn’t tell us how quickly happened

Types of Motion•Uniform motion - constant

speed in a straight line •Accelerated motion – motion

that is changing in speed or direction

•Circular motion - speed is constant but the direction of motion is changing continuously

Speed

• Speed = the distance something moves in a given amount of time• Speed is a rate; rates are when you compare a change in one quantity to

another quantity• The greater the speed, the faster it changes position• To calculate speed, you need distance and time measurements; s = d/t• The standard unit for speed is meters per second m/s• Speed is not constant• Your speed at any given moment is your instantaneous speed…

how fast something is moving at a particular instance in time• Average speed = total distance traveled / total time elapsed• Constant Speed = speed that doesn’t change

Velocity

• Velocity is speed in a certain direction…units are m/s too!

• Vector – has magnitude (speed) and direction. Velocity is a vector.

• Speed is a scalar quantity…it only has magnitude

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Acceleration

• Acceleration is the rate in which velocity changes with time, its not the same as velocity

• It is any change in velocity…when you come to a stop or turn you are accelerating

• Units of acceleration are expressed in m/s2 because it is velocity (m/s) divided by time (s)

• Free fall is an object in motion solely under the influence of gravity…9.8m/s2…which means every second speed increases by 9.8 m/s

Velocity = distance / time

(remember velocity is a vector)

Acceleration = Vfinal – Vinitial

TimeNBC Science of Football

Relative

Motion

• How an observer sees motion depends on how it compares with their motion… is called relative motion

• Relative Motion – it is described and compared to a REFERENCE POINT

• Motion is described by using a frame of reference• Look at the picture of the planes above, which is

moving?

Animations

Force• Force is a push or pull on an object In a particular direction…forces

are used everyday to change the motion of objects; Forces cause changes in speed and direction (velocity) and acceleration

• Contact forces are those that push or pull an object by touching it

• Action-at-a-distance forces are another type of force like gravity, electrical force between two charges, and magnetic force

• Forces usually act in pairs• Forces usually can’t be seen, but their effects can• Gravity is the force of attraction between two masses…the earth’s

gravity pulls on us

How Can Forces Affect Objects?• Slow them down

• Speed them up• Change their direction• Change their shape…

squeeze and tear

Force

• Like Velocity, Force is a vector…it has ? And ? To get a car from point a to point b, force must be applied in the right direction

• Net force is the overall force acting on an object when all other forces are combined…if net force = 0 then the force acting on the object is balanced

• Balanced forces have the same effect of no force at all• Unbalanced forces are needed to change an object’s

direction/motion• When two forces act in the same direction the net force is the sum

of the two forces; when unequal forces act in opposite directions the net force is the difference of the two

• The final force and direction is called the resultant force• The unit for force is the NEWTON which is equal to kg*m/s2

Animations

Newton’s Three Laws

• Sir Isaac Newton helped develop three laws to describe motion that are still in use today

• Newton’s ideas were built upon those of Galileo Galilee

• Galileo concluded that in the absence of friction, a moving object will continue to move, even if there is no force acting on it…friction stops objects in motion

Newton's 1st Law = Law of Inertia

• Objects at rest stay at rest and those moving stay moving unless there is a force acting on them…Newton’s 1st Law (Law of Inertia)

• Inertia is a resistance of an object to a change in the speed or direction of its motion…Newton’s First Law is also known as the law of inertia

• Inertia is closely related to mass…when you measure mass you are also measuring its inertia…it is easier to push a Hyundai than a Mac truck…it is harder to change the motion of an object with more mass…the more mass, the more inertia

• Slamming on the breaks in a car is an example of our inertia overcoming the force of friction on the seats

Newton's 2nd Law

• If you are to give 2 objects of different masses the same acceleration, different forces need to be applied

• Newton’s 2nd Law states that the acceleration of an object increases with increased force. Acceleration also goes up with decreasing mass…the direction of acceleration is the same as the force

• In other words, if you wanted to give two different masses different accelerations you would need to apply different forces to them

Animations

F = ma

• Force = mass x acceleration• To use this you need to understand

the units for force are called Newtons (N)

• A Newton is the amount of force needed to accelerate 1 kg of mass one meter per second (1 m/s2)…1 kg x m/s2

M = F/a a =

F/m http://www.myphysicslab.com/pendulum1.html

Newton’s Third Law

• Every action has an equal and opposite reaction = Newton’s 3rd Law

• When you stub your toe, the same force is exerted back on you as you put in

• Your chair resists the force of your body with the same push• Describes why forces act in pairs• Action and reaction forces are equal forces acting in opposite

directions on different objects

Force

Friction

• Friction is a force that resists motion between two surfaces that are pressed together. The direction of friction force is always in a direction opposing motion

• Although friction can make some tasks more difficult, most activities, like walking, would be impossible without it

• Many surfaces appear to be smooth, but when magnified, have bumps and ridges

• The type of surface, motion of the surface, and force pressing the surface together all determine the friction between objects

• Friction also produces heat• Friction created in a fluid is called drag• Friction due to the air is called air resistance

Centripetal Force

• Centripetal force is any force that keeps an object moving in a circle

• The force points toward the center of the circle

• The faster an object spins, the greater the acceleration, the greater the acceleration, the greater the force

• Likewise, the more massive an object, the more force required to keep it moving at the same speed as a less massive one

• The opposite, centrifugal force, is an outward force away from the center of rotation

Momentum

• Momentum is a measure of mass in motion…the momentum of an object is the product of its mass and its velocity

• At the same velocity, a semi-truck has more momentum than a Scooter

• You can increase momentum by increasing velocity

• Is similar to inertia; both depend on mass

• Dissimilar in that momentum has velocity

• Momentum = mass x velocity; or p = mv

• Momentum is a vector• Conservation of momentum

states that in the absence of an external force, the momentum of an object remains unchanged

• A collision is a situation in which two objects in close contact exchange energy and momentum…momentum is conserved in these collisions