Leading Ideas Newton’s 1 st law Newton’s second law Weight = mass x 10 (9.8) Difference between mass and weight
To find the weight of an object Weight = mass x acceleration of gravity On Earth: acceleration due to gravity is equal to about 10 (9.8)
Mass and Weight Mass: –Amount of stuff –Unchanging –Measure of Inertia –kg Weight: –Force of gravity –Changes because of location –N
Answers to homework 22) 10 m/s 2 23) 23 N 24) 2.1 kg 25).04 m/s 2 26) 15 N 27) 43.75 N 28) 3.7 N 29) 58.5 N
Additional Problems A 2.5 kg hula hoop is pushed forward with a force of 45.9 N. What is it’s acceleration?
Answer F = ma F = 45.9 Nm = 2.5 kg A = 45.9 / 2.5 = 18.4 m/s 2
Make up a problem Object : _______________ Amount of net force: __________ Mass of object: ____________ Solve for acceleration
Example problem A 1540 kg car starts from rest and accelerates to 50.7 m/s in 13.8 seconds. What is the net force on the car that causes this acceleration?
Answer 1540 kg = mass Rest = 0 m/s = initial velocity 50.7 m/s = final velocity 13.8 sec = time Want net force, but need to find acceleration a = (v f - v i ) / t then F net = ma a= 3.7 m/s 2 F net = 5700 N
New homework Handout #3 Working with Newton’s 2 nd Law Review conversions, acceleration All questions are in book Pg 852 3,4 Pg 857 89-95 To be handed in on Monday
To change the motion of something Need to have a net force (unbalanced forces) on the object in order to change its motion Force of rope on box Friction force
Free Body Diagrams Represent the object by a simple geometric shape or a dot Represent all forces on that object by arrows that originate from shape/dot Only represent the forces that are applied to the object, NOT forces the object applies to other things
What would be the free body diagram of ….. What are the forces on the dog?
Answer Dog Applied force of ground pushing paws forward Reactive force of ground Force of leash Weight of dog
Create a free-body diagram of one of the dancers