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Forces and Motion

Forces and Motion. W hat is Motion?. When a body is continuously changing its position with respect to the surroundings . EXAMPLES:

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Forces and Motion

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  1. Forces and Motion

  2. What is Motion? When a body is continuously changing its position with respect to the surroundings

  3. EXAMPLES: When an athlete is running on the ground then he is continuously changing his position with respect to the fans who are sitting in the stands. 2. The earth is continuously changing position with respect to sun which is “at rest”.

  4. What are the different types of motion? 1. Rectilinear Motion: when a body moves in a straight line example: an athlete running a 100 meter race along a straight track is said to be a rectilinear motion. 2. Curvilinear Motion: when a body moves along a curved path example: a planet revolving around its parent star

  5. Did you know there was a difference? • Speed- a measure of the distance an object moves in a given amount of time. Formula: S=D/t • Ex. 25 mi/hr • Velocity- an object’s speed in a particular direction • Ex. 25 mi/hr, North

  6. Acceleration- a change in speed or direction • Ex. If a car is moving 25 mph east and speeds up to 55 mph east, then the car has accelerated because its’ speed increased. • If a car is moving 25 mph east and turns to go south at 25 mph, then the car has accelerated because it changed direction.

  7. Graphing Speed: Distance vs. Time Graphs Speed = Slope = Rise/Run Rise

  8. Graphing Acceleration:Distance vs. Time Graphs • On Distance vs. Time graphs a curved line means the object is accelerating. • Curved line also means your speed is increasing. Remember slope = speed.

  9. Vocabulary Force - a push or pull • Friction - resistance to the motion • Gravity - pull towards the center of Mass, usually our Earth

  10. Newton’s Laws “If I have ever made any valuable discoveries, it has been owing more to patient attention, than to any other talent.” -Sir Isaac Newton

  11. Newton’s Laws of Motion • An object in motion tends to stay in motion and an object at rest tends to stay at rest unless acted upon by an unbalanced force. • Force equals mass times acceleration (F = ma). • For every action there is an equal and opposite reaction. http://smartweed.olemiss.edu/nmgk8/curriculum/middleschool/eighth

  12. 1st Law of Motion An object at rest tends to stay at rest. An object in motion tends to stay in motion, unless operated on by an external force. If you're going in a specific direction, unless something happens to you, you will always go that direction. Forever!!!!! • Inertia- the tendency 0f an object to continue moving or stay at rest

  13. Examples of the 1st Law of Motion • To dislodge ketchup from the bottom of a ketchup bottle, it is often turned upside down and, thrusted downward at high speeds and then abruptly halted. • Headrests are placed in cars to prevent whiplash injuries during rear-end collisions. • A space craft propelled away from the earth in a straight line will continue traveling in the same path forever. Can you give some examples?

  14. 2nd Law of Motion This law means acceleration and mass are inversely proportional. Inversely proportional means if one value goes up the other value will go down, assuming everything else stays the same. The equation: F = m * a

  15. Examples of the 2nd Law of Motion • It will take a batter more force to hit a homerun ball rather than just bunting the ball. • It will take more force to move a refrigerator than a desk. • It will take more force to stop an 18 wheeler than a car. Can you give any examples?

  16. 3rd Law of Motion For every action, there is an equal and opposite reaction. Forces are conserved. When a gun is fired, the mass of the projectile x muzzle velocity will be equal to the mass of the gun x recoil velocity. The total force involved in the situation remains the same. CONSERVATION OF MOMENTUM Formula: m1 * v1 = m2 * v2 Newton’s Cradle

  17. Momentum-how hard it is to slow down or stop an object Formula: Momentum = m x v • An object with momentum is going to be hard to stop. To stop such an object, it is necessary to apply a force againstits motion for a given period of time. • The more momentum which an object has, the harder it is to stop. Thus, it would require a greater amount of force or a longer amount of time (or both) to bring an object with more momentum to a halt.

  18. Examples of the 3rd Law of Motion • When you are swimming you push the water back and you go forward. • When you are skateboarding you push back with your foot, but you go forward. • When you are snow skiing, you push back with the ski poles and move forward. • When you skate you push back and move forward. • When you walk you are putting a force on the ground and it is putting a force on you.

  19. How does the picture below demonstrate the 3rd Law of Motion?

  20. Balanced vs. Unbalanced • Balanced Forces provide NO MOTION. • Unbalanced Forces provide motion in the direction of the greatest force.

  21. Forces That Affect Flying Lift Thrust Drag Gravity

  22. Bernoulli’s Principle –as the speed of air increases, the pressure it exerts decreases thus causing LIFT (up factor).

  23. Flight: Sideways factors • Thrust • Provided by the engines: propellers, jet or rockets • Provides forward movement for the Bernoulli lift to occur • Drag • Caused by resistance between moving surface of plane and air molecules • Friction • Opposes motion • Creates heat

  24. Gravity

  25. Facts on Gravity • Each particle of matter attracts every other particle with a force which is directly proportional to the product of their masses and inversely proportional to the square of the distance between them. • Gravitational force = (G * m1 * m2) / (d2) • Distance between masses has a MAJOR effect on the pull of gravity between the two because it is squared. • Gravity acts in BOTH directions: m1 pulls on m2 and m2 pulls on m1.

  26. Acceleration due to Gravity • Acceleration of gravity is a = 9.8 m/sec2. • Every second an object is in free fall it adds another 9.8 m/sec2 to its velocity. • Velocity will continue to increase until Terminal Velocity is reached. This is the velocity at which the resistance friction equals g. This occurs at about 200 km/hr or 120 miles/hour. • Relative gravitational force=(m1*m2)/d2

  27. Free Fall Sample problem • If an object is falling for 4 seconds, how far will it fall? • The formula for free fall is: D= ½ ( a ) t2 • D= ½(9.8m/sec2) (4 sec)2 • D= 4.9 X 16 = 78.4 m

  28. Friction

  29. Several types of Friction • Sliding Friction – when 2 solid surfaces move past each other. Example: Sand paper on wood. Lubrication is used to reduce sliding friction. • Rolling Friction – when an object rolls over a surface. Example: Wheel spinning on axel or tires on the road. Ball bearings are sometimes used to reduce rolling friction. • Fluid Friction – when an object moves through a liquid or a gas. Examples: boat moving in water and a golf ball flying through the air. Surface treatments are used to reduce fluid friction.

  30. Facts on Fiction • Friction usually opposes motion. • Sliding friction converts the energy of the motion into Thermal energy (Heat).

  31. Friction • Friction is a force that opposes motion, or makes it difficult for an object to move across a surface. • The amount of friction depends on the surface type and the force pressing two surfaces together.

  32. Space Flight • Rockets use Newton’s 3rd Law to get into the air -- Can you explain how that works? • They also use the 2nd Law. Scientist work very hard to keep the mass of the craft at a minimum. WHY? • More speed allows projectiles to travel farther, but they always fall back to earth unless they are traveling over 7900 m/sec (17,665mph) which is called is called “ESCAPE VELOCITY”

  33. Centripetal Force • The force that holds objects in circular motion is called CENTRIPETAL FORCE. • The backboard is supplying the force that is holding these people up after the floor falls. • Satellites use gravity

  34. Orbits • Low Earth orbits circle Earth in 1 ½ hours.

  35. Geosynchronous Orbit • Geosynchronous orbits 36,000 km (22360 miles) above Earth’s surface causes satellite to rotate at the same rate as Earth is revolving. • This will keep a satellite stationary above the same location on the Earth as it orbits which is best for constant communication. • 3 satellites could cover the entire Earth with delays of only seconds.

  36. What is the correct order of the following actions or principles to get a race car to full speed: • Driver checks oncoming traffic as he merges out of pit row • Newton’s 1st law • Maximum amount of fuel flows into engine • Newton’s 2nd law • Buckle the seat belt • Turn the key to crank the car • Newton’s 3rd law Correct order: e, f, g, b, d, a, c

  37. WHOOPS!!!!!!!

  38. What is the correct order of the following actions or principles to get a race car to full speed: • Driver checks oncoming traffic as he merges out of pit row • Newton’s 1st law • Maximum amount of fuel flows into engine • Newton’s 2nd law • Buckle the seat belt • Turn the key to crank the car • Newton’s 3rd law

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