1. Force and Newton’s Laws

2. Section 1 http://www.brainpop.com/science/motionsforcesa ndtime/newtonslawsofmotion/

3. 1. Distinguish between balanced and net forces. 2. Describe Newton’s first law of motion. 3. Explain how friction affects motion.

4.  What is a force?  a push or a pull  Normal force: if an object is placed on a flat surface, the normal force is straight up and is equal to the weight of the object

5.  Net force: the combination of all the forces acting on an object Same direction- add Opposite directions- subtract

6.  Balanced forces:  the forces cancel each other out  they do NOT cause a change in the object’s motion  the net force = zero  Unbalanced forces:  the forces do NOT cancel each other out,  they DO cause a change in the object’s motion

8.  If the net force acting on an object is zero, the object remains at rest, or if the object is already moving, it continues to move in a straight line with constant speed  Ex: a soccer ball sitting in the grass (at rest) and then kicked (force is applied). This causes the ball to move.

9.  FRICTION

10.  The force that acts to resist sliding b/w two touching surfaces

11.  Static friction: keeps an object at rest; caused by attraction b/w the atoms on the 2 surfaces in contact To move the object, you have to apply enough force to break the bonds.

12.  Sliding friction: slows down an object that slides; caused by microscopic roughness

13.  Rolling friction: needed to make a wheel/ tire turn; keeps the tire from slipping on the ground

14.  pull a wagon with wheels or a wagon with no wheels? Why?  A wagon with wheels because the rolling friction between the wheels and the ground is less than the sliding friction between the bottom of the wagon and the ground.

15. Section 2

16. 1. Explain Newton’s second law of motion. 2. Explain why the direction of force is important.

17.  Connects force, acceleration and mass  An object acted upon by a force will accelerate in the direction of the force The force needed to change the motion of an object depends on its mass. Predict which grocery cart would be easier to stop.

18.  Acceleration= net force/ mass  F net a = ______ or F net = ma m  Units  Acceleration: m/s 2  Net force: Newtons (N)  Mass: kg

19.  It exists between any two objects that have mass  Between you and your chair you and your table, the table and the chair, etc  These gravitational forces are weak b/c their masses are small  What happens to a ball when you throw it horizontally?  What would happen if gravity did not exist?  http://www.brainpop.com/science/motionsforcesandti me/gravity/ http://www.brainpop.com/science/motionsforcesandti me/gravity/

20.  Earth’s gravitational pull on us is large enough to notice b/c the Earth’s mass is HUGE!!!

21.  What other object in the solar system has a HUGE MASS?  The Sun!  The Sun’s gravitational pull on us is not noticeable, b/c it is too far away; gravitational forces decrease with distance

22.  Weight – gravitational force between an object and Earth.  Your weight would be different on another planet because every planet has a different gravitational force.  Your mass is always the same

23.  Increases as you move faster  Which would move faster a crumpled paper or a flat paper?

24.  A net force of 4,500 N acts on a car with a mass of 1,500 kg. What is the acceleration of the car? 1. State the formula 2. Insert info 3. Solve & Units F net ma

25.  A book with a mass of 2.0 kg is pushed along a table. If the net force on the book is 1.0 N, what is the book’s acceleration? 1. State the formula 2. Insert info 3. Solve & Units F net ma

26.  A baseball has a mass of 0.15 kg. What is the net force on the ball if its acceleration is 40 m/s 2 ? 1. State the formula 2. Insert info 3. Solve & Units F net ma

27. Section 3

28. 1. Identify the relationship between the forces that objects exert on each other.

29.  Forces always act in equal but opposite pairs  “For every action, there is an equal but opposite reaction”  EX: When you push on a wall, the wall pushes back on you with the same amount of force you exerted on the wall

30. Demonstration #3

31.  Newton’s 1 st Law of Motion

32.  Newton’s 2 nd Law of Motion

33.  Newton’s 3 rd Law of Motion