The Questions. 1. What does Net Force mean? 2. What is Newton s 1 st Law?

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1 The Questions 1. What does Net Force mean? 2. What is Newton s 1 st Law?

2 Force changes motion A force is a push or pull BUT IT IS THE NET FORCE THAT WE CARE ABOUT!!

3 Net Force Net Force is the sum of the forces acting on an object in EACH direction (x or y). What is the Net Force acting on the golf ball?? x-direction: (+20N) + (-10N) = +10N y-direction: (+5N) + (-5N) = 0N +20N -5N +5N Gravity -10N

4 (+300N) + (+300N) = +600N (+Normal Up) + (-Gravity down) = 0N Is this object in Equilibrium?

5 Newton s 1 st Law: The Law of Inertia Official Version: An object at rest will stay at rest and an object in motion will continue in motion at a CONSTANT VELOCITY unless acted on by a NON-0 Net force.

6 Newton s 1 st Law: The Law of Inertia Newton s 1st Law in simple English: Objects that are not moving will not move unless pushed by a non-0 NET force. Objects that are moving will keep moving at the same velocity unless a non-0 NET force pushes on them. If the Net Force on an object is 0N, an object at rest (velocity=0m/s) will stay at rest (velocity=0m/s). If an object is acted upon by an unbalanced force (Net Force 0), its motion (VELOCITY) will change.

7 Newton s 1 st Law: The Law of Inertia Newton s First Law Simple English: Objects that are not moving will not move unless pushed by a not-0 Net Force. Objects that are moving will keep moving at the same velocity (a = 0) unless a not-0 Net Force pushes on them. If the Net Force on an object is 0N, an object at rest (v = 0m/s) will stay at rest (v=0m/s). If a non-0 Net Force pushes on an object its velocity will change (acceleration will not be 0).

8 Newton s 1 st Law: The Law of Inertia Inertia is a property of matter! Who said this?? Billy Nye Inertia is the property of an object that resists changes in motion (VELOCITY). Inertia = mass Inertia is the same thing as an objects mass. Which ball has more inertia? Inertia is measured with kilograms.

9 The Answers 1. What does Net Force mean? a) The sum of all of the forces acting on an object. 2. What is Newton s 1 st Law? a) Known as the Law of Inertia b) An object s velocity will change if the Net Force is not 0.

10 The Questions 1. What is Newton s 2 nd Law? 2. How do we use Newton s 2 nd Law? 3. What is weight?

11 Newton s 2 nd Law: a = F net /m Newton s 1 st Law says that an object s velocity will only change if there is a non-0 Net Force acting on an object. Newton s 2 nd Law: the amount of velocity change (acceleration) an object will have depends on the Net Force acting on the object divided by the mass of the object. a = F net / m Another way to write this is: F net = m a a=acceleration, F net = Net Force, m = mass of object

12 Newton s 2 nd Law: a = F net /m There are 3 main ideas related to Newton s 2nd Law: 1. Non-Zero Net Forces lead to changes in the velocity of an object (acceleration). 2. A larger net force on an object causes a larger acceleration of the object. 3. Mass effects acceleration: i. Bigger mass means smaller acceleration. ii. Smaller mass means larger acceleration.

13 The Unit of Force: Newton (N) The S.I. unit of force is the Newton. A newton is the amount of force needed to accelerate a 1kg object by 1m/s 2.

14 Newton s 2 nd Law: a = F net /m The 2 nd Law says that a = F/m The greater the Force, the higher the acceleration. Lower Force, lower acceleration.

15 Newton s 2 nd Law: a = F net /m The greater the mass, the smaller the acceleration from the same net force.

16 Newton s 2 nd Law: a = F net /m Keep the following important ideas in mind: 1. A non-0 Net Force is what causes acceleration. 2. If there is no acceleration, the Net Force must be zero. 3. If there is acceleration, there must be a Net Force. 4. The unit of Newtons is based on kilograms, meters, and seconds.

17 Solving Problems Try to figure out these problems!! C Level: What acceleration does a 400kg object have if a net force of 1400N is applied to that object? Solution: 3.5m/s 2

18 Solving Problems Try to figure out these problems!! B level: What Net Force is needed to give a 850kg object an acceleration of 4m/s 2? Solution: 3400N

19 Solving Problems Try to figure out these problems!! A Level: A 5000N car starts from rest and is moving at a velocity of 20m/s after 5 seconds. The engine produces a thrust of 4500N and there is 1000N of friction acting on the car. What is the mass of the car? Solution: 875kg

20 The Answers 1. What is Newton s 2 nd Law? a = F/m 2. How do we use Newton s 2 nd Law? Identify the Net Force. Plug into the equation.

21 Newton s First Law is known as: 1. Law of Action and Reaction 2. Law of Conserved Mass 3. Law of Inertia 4. Law of Conserved Energy 5. Law of the Benevolent Dictator Law of Action... 0% 0% 0% 0% Law of Conserv... Law of Inertia 100% Law of Conserv... Law of the Ben...

22 Inertia is measured in units of 89% 1. Meters 2. Liters 3. Kilograms 4. Seconds 5. N/kg 6. m/s 2 5% 5% 0% 0% 0% Meters Liters Kilograms Seconds N/kg m/s2

23 What has more Inertia? 94% 1. Baseball 2. Skyball 3. Bowling Ball 4. Beach Ball 5. Golf Ball 6. Ping Pong Ball Baseball 6% Skyball 0% 0% 0% 0% Bowling Ball Beach Ball Golf Ball Ping Pong Ball

24 A Net Force of +100N acts on an object. That object will 1. Stay in motion. 2. Stay at rest. 3. Have its velocity changed. 83% 17% 0% Stay in motion... Stay at rest. Have its veloc...

25 The Questions What is Newton s 3 rd Law? Forces always occur in what?

26 Newton s 3 rd Law Newton s 3 rd Law says that for every action force there must be an equal and opposite reaction force. The reaction force must be equal in strength and opposite in direction. There can never be a single force, alone!! Forces always occur in pairs.

27 Newton s 3 rd Law Newton s Third Law (action-reaction) applies when a force is pushed (or pulled) on any object, like a door. exerted a force on the door. And The door exerted a force on.

28 Newton s 3 rd Law When figuring out action and reaction forces it is helpful to draw a picture. The action force (thing that is doing something) is the. The reaction force (force that happens because of the thing that is doing something) is the.

29 Newton s 3 rd Law ractives/literacy/newton/newton. html

30 A woman with a weight of 500N is sitting on a chair. Solving Problems Describe one actionreaction pair of forces in this situation. Give the magnitude of each force and what object the force acts on.

31 What is Newton s 3 rd Law? For every action force there is an equal and opposite reaction force. The Answers Simple English: Forces always occur in pairs and act on different objects. Forces occur in pairs.