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Transcript
FORCES AND PRESSURE I. Laws of Motion A. Law of Inertia B. Law of ______________ C. Law of _____________ All introduced by Sir Isaac Newton II. Force and Motion ( 1-1 pgs 22-30) Speed, Velocity, Acceleration and Motion A. SPEED Tells you how fast an object is moving Distance d Speed = -------------- = ---Time t EX: If you travel 130 miles in 2 hours, what was your average speed? Formula: Substitution: Answer and Label: Speed = d t B. VELOCITY Tells you how fast and in what direction an object is moving. d Velocity = -------------- = ---- direction Distance Time t EX: What is your velocity if it takes you 25 hours to drive 1,000 miles to Orlando, Florida? Formula: Velocity = d t Substitution: Answer and label: C. ACCELERATION: speeding up slowing down a change in direction change in velocity v Acceleration = -------------- = ---Time t direction EX: If a car goes from 0 mph to 60 mph in 10 seconds, what is its’ acceleration? Formula: A = v t Substitution: Answer and Label: Practice- remember: Formula, substitution, labeled answer. TRY: If you travel 160 miles and it takes you 4 hours, what is your speed? TRY: If you travel 3,500 miles to Disneyland in California And it takes you 50 hours, what is your velocity? TRY: If you accelerate to pass a car and your speed goes from 50 to 70 miles per hour in 5 seconds, what is your acceleration? TRY: If you travel 90 miles to Canada and it takes you 1.5 hours, what is your velocity? D. INERTIA (Idle or lazy) The tendency of an object to resist changes in motion. Objects seem _________ because they do not easily change the way they __________. Objects at rest don’t want to start ________, objects moving do not want to ___________. 1. MASS (effects on inertia) Q. Is it easier to move a large truck or a small car? Therefore: the more mass you have the greater the inertia. TRY: Which has greater inertia? a) A pillow or a toaster? b) A balloon or a brick? c) A desk or a chair? d) A refrigerator or a stove? E. NEWTON’S FIRST LAW OF MOTION An object will remain at rest and an object in motion will remain in motion at a constant velocity UNLESS it is acted on by an outside force. A force is a push or pull on matter. 1. Interactions that push or pull A. FRICTION o A force that resists motion between two objects in contact with each other. Q: What might be some important aspects of friction? B. GRAVITY o A force of attraction between any two objects caused by their masses. o As the mass _________, so does the __________. o All objects accelerate towards earth at the rate of 9.8 m2 unless acted upon by air resistance. s EXTRA: A feather would fall as fast as an elephant IF there was no air resistance!!!! III. 1-2 How forces act on objects (pg. 31-38) A. NEWTON’S SECOND LAW OF MOTION:Momentum 1. Formula: Force = Mass ● Acceleration This means a force causes a mass to accelerate If the mass is large, you will need a large force to move it If you want to accelerate quickly, you will need a larger force Law of Momentum: F=M●A Units used: 1. 2. Mass kg Acceleration m s2 3. Force kg/m/s/s also called a NEWTON (N) EX: What amount of force would have to be applied to a 15 kg mass to accelerate it 6 m2 ? s Formula: F = m ● a Substitution: In class activity Mr. King 1. What is the force required causing an acceleration of 16 m in a 4 kg mass? s2 2. What is there force required to cause an acceleration of 7 m in an 18 kg mass? s2 3. A force of 30 N is exerted on a 5 kg mass. What is the object’s acceleration? 4. A force of 40 N is applied to a mass and causes an acceletration of 8 m . What is the object’s mass? s2 5. What is the weight of a 10 kg mass? 6. How much force must you exert to hold a 10 kg mass at one height? B. NEWTON’S THIRD LAW OF MOTION: For every ACTION FORCE there is an equal and opposite REACTION FORCE. 1. ACTION FORCE - a push or pull on matter 2. REACTION FORCE – the force that pushes back on you at the exact moment. EX: rocket Balanced Force: When the force on one side of an object is equal to the force on the other side of the object. There will be NO acceleration. EX: book Unbalanced Force When the forces acting upon an object are not equal There WILL be acceleration…a change in motion Weight The gravitational force acting on an object Falling objects accelerate at the rate of 9.8 m s2 Momentum Momentum = M●V When the mass is large, momentum is ____________ When the velocity is large, momentum is ___________ EX: Shooting a bullet vs throwing a bullet Concept Map of the Laws!!!! Newton’s Laws of Motion Homework: Newton’s Laws Name ______________ Identify which of Newton’s Laws of Motion each of the following is the BEST example of. Write either: I, II, or III. _____ 1. The Voyager satellite needed no fuel supply to CONTINUE MOVING past Uranus after it left Earth. _____ 2. Using the SAME BAT a baseball player can hit a baseball further than a softball. _____ 3. You must use MORE FORCE to move a sled with someone on it than when it is empty. _____ 4. Pulling BACK on the oars moves a boat FORWARD. _____ 5. The EXHAUST of a jet engine move the airplane FORWARD. _____ 6. You are thrown in to the door when a car CHANGES DIRECTION. _____ 7. Which law explains the action occurring in the diagram below: _____ 8. Which of Newton’s Laws explains why the skateboard doesn’t go with the skater when he pushes off? 1-3 Pressure and Buoyancy (p. 39-45) Pressure- the weight or force acting on each unit of area Pressure = Force Area Ex: How much pressure does 80N of force exert on 5 cm2? It is different with fluids--- the pressure exerted by a fluid depends on the height of the column of water above the object. Shallow water can not exert much pressure on you because there is not much water above you. The deeper you dive in water the taller the column of water above….thus the more pressure it exerts on you. Why you float……. When you get into water you displace water (move the water out of the way) the volume of the water displaced is equal to the volume of the object that is submerged. Archimedes – Greek mathematician discovered in the 3rd century the following concept…. “the weight of water displaced by an object is equal to the amount of weight lost by the object” In other words, big objects displace a lot of water AND water weighs a lot…..so the more water you displace, the more weight you will reduce in the water. Another concept…. If you “lose” 25 pounds while you are in a pool, it is because water is also pushing up on you with a force of 25 pounds. This force is called…. Buoyant Force—upward force exerted by water (or any other fluid) that is equal to the weight of the water the object is displacing. In- class worksheet Pressure 1. How much pressure does 80N of force exert on an area of 16cm2? 2. How much pressure does 120N of force exert on an area of 12 cm2? 3. How much pressure does 450N of force exert on an area of 100cm2? 4. An elephant applies a pressure of 60N/cm2 and uses a total surface area of 500cm2. Calculate the force the elephant needed to exert this kind of pressure?