Transcript Slide 1
2*3 Newton’s 2nd Law: Push or Pull WDYS? (p157) 1. Person #1 = 2. Person #2 = 3. Person #3 = WDYT? 1. Force is _____. 2. The same force on a tennis ball will be (the same/ different) on a bowling ball because _____. 2*3 Investigate (p157) I will use a flexible ruler to continuously push a car across a table or floor. 1. Small Bend = _____ Large Bend = _____ 2a. Push car with a small force…the car continually _____ its speed as the force is applied. 3a. Push car with a large force…the car continually _____ its speed as the force is applied. 2*3 Investigate (p157) 3b. Smaller bend = _____ acceleration Larger bend = _____ acceleration 3c. Acceleration was _____ with a larger bend 3d. The greater the bend (force) pushing the object, the _____ the acceleration 2*3 Investigate (p157) Now use a SMALLER mass 4a. With a LARGE bend (force ) by the ruler, the smaller object will experience a __________ acceleration than when using the previous car. Now use a LARGER mass 5a. With a LARGE bend (force) by the ruler, the larger object will experience a __________ acceleration than when using the previous car. 2*3 Investigate (p157) 5b. When equal amounts of a constant force are used to push objects having different masses, the more massive object will have _____ acceleration. 6a. If you push a larger object with a small force, then the acceleration would be _____. 6b. If you push a smaller object with a large force, then the acceleration would be _____. Physics Talk (p160-167) 1. Newton’s 2nd Law of Motion You observed: 1. a constant force produces an acceleration (direct) 2. acceleration decreases with an increase in mass (indirect) Newton’s 2nd Law of Motion a is directly proportional to F and indirectly related to m, and the direction of a is the same as F Newton (N) is the SI unit for Force; it is equal to (kg * m/s/s) Physics Talk (p160-167) acceleration = Force / mass a=F/m F=m×a m=F/a Units for acceleration (a) = m/s/s km/h/h Force (F) = Newton (N) mass (m) = g kg Physics Talk (p160-167) As the result of a serve, a tennis ball (m=.058kg) accelerates at 430m/s/s for the very brief time in contact with the racket. a) What is the force? b) Could an identical force accelerate a 5kg bowling ball at the same rate? Physics Talk (p160-167) 1. A tennis racket hits a sand-filled tennis ball (m=275g) with a force of 40N, what is the acceleration? 2. A weightlifter raises a 440kg barbell with an acceleration of 2m/s/s, how much force does the weightlifter exert on the barbell? 3. Iceman creates an ice all and throws it with an acceleration of 28m/s/s. The force of the ice ball hitting Magneto is 115N, what is its mass? 2*3 TOTD 1. The Newton (N) is = _______________. 2. If there is a large Force on a LARGE massive object, then the acceleration will be __________. 3. If there is a large Force on a SMALL massive object, then the acceleration will be __________. 4. What is the acceleration of a 0.6kg volleyball when a player uses a 84N force to spike the ball? 5. What force would be needed to accelerate a 0.08kg golf ball at 40m/s/s? Physics Talk (p160-167) 2. Gravity, Mass, Weight, and Newton’s 2nd Law Newton’s 2nd Law if there is an acceleration, then there is an unbalanced force acting on the object In 2*2 Investigate, the bending ruler was due to the force of gravity 9.8m/s/s Weight is the force of gravity acting on an object, where the equation is w = m × g Physics Talk (p160-167) 3. Balanced and Unbalanced Forces The direction AND magnitude of the forces determine the motion of the object: a) Both forces in SAME direction = ADD b) Forces are in OPPOSITE direction = SUBTRACT Free-Body Diagram used to show the size and direction of ALL forces acting on an object Checking Up (p167) 1. Newton’s 2nd Law of Motion states ___. 2. For a constant force, increasing the mass of an object will __________ its acceleration. 3. The statement means that there will be a _______________ acting downward on the mass due to force of Earth’s __________. 4. Your weight would __________ while your mass would __________. PTG (171-173) Force (N) mass (kg) acceleration (m/s/s) ? 70kg 5m/s/s 800N ? 10m/s/s 70N 7kg ? 400N ? 5m/s/s -1500N 100kg ? ? 100kg -30m/s/s PTG (171-173) 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. On previous slide or on page 171 do not do a= F= do not do F= a) Weight = lbs * 4.38N/lbs = b) m= do not do No, the force of your hand stops acting on the ball the moment the two are _____. Draw a free-body diagram with forces labeled Draw a free-body diagram with forces labeled a= 2*3 TOTD 2