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Physical Science Chapter 1

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 Science Chapter 1

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  1. Physical ScienceChapter 1 Motion

  2. 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.

  3. 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

  4. 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

  5. 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

  6. 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

  7. 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

  8. 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)

  9. 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.

  10. 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

  11. 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

  12. 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

  13. 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

  14. 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

  15. 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!!

  16. 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)

  17. 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

  18. Your weight on other planets& 3 different types of stars

  19. 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

  20. 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

  21. 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.

  22. 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.

  23. 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.

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