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Physical Science Chapter 1. Motion. Are You Moving ?. You are sitting down, reading a book…. Are you moving? Object is in motion when its distance from another object is changing. All depends on the “Point of Reference”
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Physical ScienceChapter 1 Motion
Are You Moving ? • You are sitting down, reading a book…. • Are you moving? • Object is in motion when its distance from another object is changing. • All depends on the “Point of Reference” • Therefore object is in motion if it changes position relative to a reference point.
International System of Units • “SI” • Based on the number 10 • Distance (length) uses meter (about 39 inches) • Mass (how much matter) uses gram ( a nickel is about 5 grams) • Volume (how much space) • Liquid volume – uses liter ( a little more than a quart) • Solid volume – uses cm3( about the size of a sugar cube) • 1 ml = 1 cm3 • Weight (affect gravity has on object) uses newton ( an apple weighs about 1 newton) (1 pound is about 4.4 newtons) • Density = Mass / Volume = grms / ml
Metric Stairs • You should be comfortable with converting from [cm] to [m], [mm] to [km], and so on. Convert: 1527 centigrams into hectograms: going four steps up means you move the decimal 4 places to the left. Therefore: 1527 centigrams = .1527 hectograms & 9.8712345 kg = (steps to the right) 9871234.5 mg
Speed = distance / time • Formula: S=D/T • What is the speed of a car that traveled 75 km in 1.5 hr? S = D / T = 75km / 1.5 hr = 50 km/hr • Tells only a magnitude (how much) • Distance units include: inches (in), feet (ft), miles (mi),meters (m), kilometers (km), centimeters (cm), light year, etc. • Time units include minutes (min), seconds (sec), hours (hr), years (yr), etc. • Speed can be any distance unit divided by any time unit!! • Mi/hr, ft/sec, km/min Velocity is speed with a direction • Written like: 125 miles/hour east or 83 m/sec towards the house • What is the velocity of a jet that traveled 1623 mi North in 83 min? • V = D / T = 1623 mi / 83 min = 19.5 mi/min North
Average Speed or Average Velocity • Average speed = total distance / total time What is the average speed after 2 minutes? total distance is 75m, total time is 2 minutes. S = D/T S = 75m / 2min S= 37.5 m/min What is the average speed between 2 & 4 minutes? total distance: 110m – 75m = 35m total time: 4min – 2min = 2minutes total time S = D/T S = 35m / 2min S= 17.5 m/min
Acceleration • The change in speed or velocity over time • In scientific community, the symbol for “change” is the triangle: • Change in velocity is found by subtracting the final speed from the initial speed Vf - Vi = V The formula for acceleration is: A = Vf - Vi= V time time Therefore the units for acceleration are going to be a distance/time/time Example ft/min/sec
Acceleration • For an object to accelerated it must: • Speed up (positive acceleration) • Slow down (negative acceleration a.k.a deceleration ) • Change direction of travel 3 1 2 Each of these pictures depicts a type of acceleration: 1: the shuttle is speeding up every sec of the flight into orbit 2. the horse has come to a screeching halt (slowing down) 3. the baseball thrown to the batter is hit into the outfield (changed direction)
What’s it mean? • What does a = 5 [m/sec2] mean? • If an object starts at rest, its velocity increases by 5 [m/sec] every second. Therefore, an object accelerating at 5m/sec2 will be travelling at 20 m/sec after 4 seconds.
The Nature of Force A Push Or A Pull • By definition, a Force is a push or a pull. Just like Velocity & AccelerationForces have both magnitude and direction components
Balanced & Unbalanced Forces • With a Balanced force – opposite and equal forces acting on the same object result in NO motion of the object • Unbalanced forces – two or more forces of unequal strength or direction acting upon on an object results in the motion of the object
Vectors • Vectors are a method used to visually show forces • A vector is a quantity which has both magnitude (size) and direction. • The length of the arrow shows the magnitude of the vector. • The angle of the arrow shows the vector's direction. • Just like numbers, we can add two or more vectors together and get a net force called the resultant
Adding 2 or More Vectors Fig 1 Fig 3 Fig 2 • Add vectors A and B to get the Resultant C • A + B = C • Fig 1 - shows the magnitude & direction of the 2 vectors we are adding • Fig 2 – we move the beginning of vector B to the end of Vector A, making sure to keep the magnitude & direction exactly the same • Fig 3 – Connect the beginning of Vector A to the end of Vector B, this is your “Resultant” C. Click the icon to run java script game that allows you to add vectors
Newton’s 3 Laws of Motion • Newton’s 1st Law of Motion: • AKA The Law of Inertia • which states an object at rest will remain at rest, and an object in motion will remain in motion at a constant velocity until acted on by another force. Remember: The greater the mass of an object the greater the inertia
Newton’s 3 Laws of Motion • Newton’s Second Law of Motion aka F=ma • Force = mass x acceleration • Can be written as: • F=ma ; a= F/m ; m= F/a • What is the basic unit for mass? Kilogram • What is the basic unit for acceleration? Meter/sec/sec • Therefore the basic unit for Force is (kilogram)( meter/sec/sec) • An object with a mass of 1 kg accelerating at 1 m/s/s has a force of 1 Newton Ding-a-ling!!
Newton’s 2nd Law & Force of Gravity • Everyone has heard of the FORCE of gravity • So far, we know only of four types of fundamental forcesin nature: • Gravity, Electromagnetic, Weak, and Strong • Gravity: the force that pulls objects towards each other • Since gravity is a force it also obeys Newton’s second law F=ma Since objects fall at the same speed, their acceleration is the same. All objects accelerate at the rate. Here on Earth the rate is: Ag=9.8 m/s2 Or Ag=32 ft/s2 With this experiment, Galileo proved Aristotle wrong Air resistance keeps things from falling equally With this experiment, Apollo 15 astronauts proved Galileo right. (link to You Tube)
Newton’s 2nd Law & Weight • F=ma • Weight is the force of gravity acting on an object’s mass. • Therefore weight is a type of Force • The formula for weight: Weight = mass x Ag • Since Ag= 9.8 m/s2 then Weight = mass x 9.8 m/s2 Remember: 1 newton = 0.22 pounds
Newton’s 3 Laws of Motion • Newton’s 3rd Law of Motion: • For every action there is an equal & opposite reaction. • If an object is not in motion, then all forces acting on it are balanced and the net force is zero! • Friction – the force that one surface exerts on another when the two rub against each other. Fluid friction Sliding friction Rolling friction
Momentum • An object’s momentum is directly related to both its mass and velocity. • Momentum = mass x velocity • For some reason, maybe because mass is designated as “m” in formulas, momentum is designated as “p”. • Therefore: p = mv • The unit for mass is kg, the unit for velocity is meter/second, therefore the unit for momentum is kg m/sec • Conservation of Momentum: • When two or more objects interact (collide) the total momentum before the collision is equal to the total momentum after the collision
Momentum – 2 moving objects • During this collision the speed of both box cars changes. The total momentum remains constant before & after the collision. The masses of both cars is the same so the velocity of the red car is transferred to the blue car.
Momentum – 1 moving object • During this collision the speed red car is transferred to the blue car. The total momentum remains constant before & after the collision. The masses of both cars is the same so the velocity of the red car is transferred to the blue car.
Momentum – 2 connected objects • After this collision, the coupled cars make one object w/ a total mass of 60,000 kg. Since the momentum after the collision must equal the momentum before, the velocity must change. In this case the velocity is reduced from 10 m/sec. to 5 m/sec.