Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Mechanics of planar particle motion wikipedia , lookup
Electromagnetism wikipedia , lookup
Artificial gravity wikipedia , lookup
Coriolis force wikipedia , lookup
Modified Newtonian dynamics wikipedia , lookup
Lorentz force wikipedia , lookup
Fictitious force wikipedia , lookup
Centrifugal force wikipedia , lookup
Net Force Net force is the sum of the forces acting on one object. Sigma , Ʃ, is the Greek symbol used to express addition. Fnet = Ʃ F which means.... Fnet = F1 + F2 + .... ex. Ms. Curtis pushes her trolley eastward, against friction. How would you calculate the net force acting on the trolley? FBD Fnet = Ʃ F = Ff + FA + FN + Fg motion However, we can only add linear vectors like normal integers. FN Ff FA So, we will break the problem into the horizontal and the vertical vectors. Fg Fnet y = Ʃ F y Fnet y = Fg + FN Fnet x = Ʃ F x Fnet x = FA + Ff motion FN Ff FA Fg Calculate the net force on the following objects: FA1 a) FA1 = 15.8 N [up] FA2 = 12.3 N [up] Fg = 16.9 N [down] = 16.9 N [up] FA2 motion work in one direction Fg Fnet y = Ʃ Fy = FA1 + FA2 + Fg = 15.8 N + 12.3 N + ( 16.9 N) = 11.2 N [up] No horizontal forces here. So all of the given forces are included in the vertical net force. FN motion b) Ff Fa Fg Fnet x = FA = 35.98 N [E] Fg = 63.90 N [down] = ___ FN = 63.90 N [up] Ff = 10.17 N [W] = _______ work in [E] and in [up] Fnet y = Did you provide equations? Did you show substitutions? FN c) FA1 FA2 Ff Fg1 Fg2 Fnet x = F net y = motion FN = 12.32 N [up] FA1 = 9.05 N [N] FA2 = 10.82 N [N] Fg2 = 3.87 N [down] Fg1 = 2.55 N [down] Ff = 8.33 N [S] Net force is important because it causes objects to accelerate. The direction of the net force determines the direction of the acceleration. Fnet Fnet ex. Fnet accel accel accel Fnet accel Draw an arrow to represent the direction of the acceleration. Predict if the following objects are speeding up, slowing down, or moving at constant velocity. F net a) motion F net b) motion c) motion F net d) motion F net acceleration Object is speeding up because the acceleration is in the same diection as the motion (or velocity vector). Newton's Second Law of Motion: The net force acting on an object is equal to the product of the object's mass and the object's acceleration. (Note, the net force causes the acceleration. The acceleration does not cause the net force.) important equation F net = m a If the net force is horizontal (ex. east), then the acceleration will also be horizontal (ex. east). F net x = m a x If the net force is vertical (ex. up), then the acceleration will also be vertical (ex. up). F nety = m ay ex. A ball of mass 86 g is pushed by a net force of 9.03 N east. What is the acceleration of the ball? m = 86 g = 0.086 kg Fnet = 9.03 N [E] a = ? F net x = m a x a x = F netx m 2 = 105 m/s2 = 1.1 x 102 m/s [E] = 9.03 N 0.086 kg noticed direction of net force was horizontal mass must be in kilograms ex. What net force is needed stop a 703 kg car, moving east, at a uniform acceleration of 8.663 m/s2? m = 703 kg a = 8.663 m/s2 [E] stopping implies acceleration is opposite to the direction of motion F netx = m ax = (703 kg) ( 8.663 m/s2) = 6090.089 N = 6.09 x 103 N [E] net force acts in the direction opposite to the car's motion Text Reading p. 145 p. 161 p. 162 note, book did write net force.....we will Try problems on the Introduction to Newton's Second Law Some of the answers are provided in another link. Watch units carefully! PHY 521 Newton’s Second Law: An Introduction 1. What is the net force acting on a 20 kg object if the object is accelerating at 0.28 m/s2, west? 2. What is the net force acting on a 20 kg object if the object is accelerating at 5669 km/h2, east? 3. What is the acceleration of a 3 g penny if a net force of 50 N [E] acts on it? 4. What is the acceleration of a supertanker of mass 1.6 x 10 8 kg if a net force of 50 N [E] acts on it? 5. On the Superman roller coaster, you are able to experience an acceleration of 4.5 |g| for an instant. If |g| = 9.81 m/s2, what is the size of the net force acting on a person of mass 65.0 kg ? (hint........ size of a = | a| = 4.5 ( 9.81 m/s2) = ?? ) 6. A person accelerating at 9.81 m/s2, down, as she falls out of a plane experiences a net force of 1.0 x 10 3 N, down. What is her mass? 7. A supertanker of mass 1.0 x 10 8 kg accelerates from rest reaching a velocity of 4.1 km/h south after traveling 3.5 km south. What is the net force acting on the supertanker? 8. If it takes a human cannonball 1.5 s to exit a 1.6 m long cannon (pointing north), what is the average net acting on the performer if his mass is 65 kg? force 9. A bicycle of mass 14.6 kg and a rider of mass 50 kg experience a net force of 12 N, west. What is their 2.0 s after they start moving? (hint....What is the total mass being accelerated?) velocity Answers: 1. 5.6 N [W] 2. 8.8 N [E] 2 3. 2 x 10 4 m/s [E] 2 –7 4. 3.0 x 10 m/s [E] 3 5. 2.9 x 10 N 6. 1.0 x 10 2 kg 7. 1.9 x 10 4 N [S] 8. 92 N [N] 9. 0.38 m/s [W] Attachments Shopping Cart Truck Mishap.mp4