The Laws of Motion

1. The Laws of Motion Chapter 2

2. What causes these riders to move around? What prevents them from falling out? How do forces change the motion of the riders?

3. Types of forces • Force- a push or pull on an object, all forces have strength and direction. • Contact force- a push or pull on an object by another that is touching it. Non-contact force- a force that one object can apply on another without touching it. Examples- magnetism, Electricity and Gravity.

4. GRAVITY • Gravity- is an attractive force that exists between all objects that have mass. • Mass- The amount of matter in an object

5. The law of Universal gravitation • Issac Newton, an English Scientist and Mathematician, developed the law of universal gravitation. • This law states that all objects are attracted to each other by a gravitational force. • Gravitational force between objects decreases as the distance between the objects increase. • When the mass of an item increases the force between them alos increases. • All forces are measured in Newtons.

6. Weight- a gravitational force • Weight is a gravitational force exerted on another object. • Weight is proportional to mass. On Earth, the weight of an object in Newtons is 10X the object’s mass in Kilograms. • Near Earth’s surface , an objects weight is the gravitational force exerted on the object by the Earth.

7. FRICTION- a force that resists the motion of two surfaces that are touching. • Static Friction- prevents surfaces from sliding past each other. • Sliding Friction- opposes the motion of surfaces sliding past each other. • Fluid Friction- friction between a surface and a fluid

8. Describe a time when you have experienced gravity, static friction, and sliding friction.

9. What causes friction? Microscopic bumps and dips on surfaces that touch each other and weak electrical charges on the surface. What Reduces Friction? Lubricants. They separate the surfaces that are in contact with each other.

10. Newton’s First Law of Motion • Net force- The combination of all the forces acting upon an object. • To understand the motion of an object, you need to understand the forces acting on it. Besides flying, what are some of the actions that require the osprey to exert force? Why does spreading her wings increase the osprey’s air resistance? Compare an ospreys wings and a parachute from a sky diver.

11. A reference direction- a direction that you choose from a starting point to describe an object’s position. • When you combine forces in two opposite directions, one force is positive and the other force is negative. • When forces in the same direction combine, the net force is also in the same direction. The sum of the net force is the sum of the forces. What forces can act on an object at a given time? Gravity, friction, and applied force

12. Balanced forces- forces acting on an object that combine and form a net force of zero. • Unbalanced forces- forces acting on an object that combine and form a net force that is NOT zero.

13. Newton’s first law of Motion- states that if the net force of an object is zero, the motion of the object doesn’t change.

14. When balanced forces act on an object, the objects velocity does not change. • If unbalanced forces act on an object at rest, the object will start moving. • If unbalanced forces act on a moving object, the object will change its velocity.

15. Inertia-the tendency of an object to resist a change. When a car stops short, a person continues moving forward because of its inertia. A book sitting on a table stays in place because of inertia.

16. How do forces change motion? • Forces change an objects motion by changing its speed, its direction, or both. • Only unbalanced forces change the velocity of an object. • Unbalanced forces are acting on an object that is at rest when the object starts moving. • Unbalanced forces change the velocity of a moving object. • Another name for change in velocity over time is acceleration. • Unbalance forces can make an object accelerate by changing the object’s speed, direction or both.

17. Newton’s second Law- states the acceleration of an object is equal to the net force acting on the object divided by the object’s mass. • Forces change an object’s motion by changing its speed, its direction, or both its speed and direction. • When Unbalance forces act on an abject at rest, it moves in the direction of the net force. Unbalanced forces cause an object to speed up or slow down.

18. Make up a story problem that uses Newton’s second Law of Motion.Problems should require solving for force, mass or acceleration using the equation a=f/m

19. If you throw a .5kg basketball with a force of 10N. What is the acceleration of the ball?

20. Circular motion-is any motion in which an object is moving in a curved path. • Centripetal Force-In a circular motion, a force that acts perpendicular to the direction of motion, toward the center of the curve

21. Newton’s Third Law • When one object exerts force on a second object, the second object exerts an equal force in the opposite direction on the first object. • When one object exerts a force on another object, the second object exerts a force on the first object in the opposite direction.

22. Using Newton’s Third Law of Motion • When you push against an object, the force you apply is called the action force. • Newton’s third law establishes that the object you push on applies an equal and opposite reaction force against you. • According to Newton’s second Law, when the reaction force results in an unbalanced force, there is a net force and the object accelerates.

23. Momentum • The measure of how hard it is to stop a moving object. • Momentum is the product of an object’s mass and it’s velocity. • What is the momentum of a 12 kg bicycle moving at 5.5m/s?

24. The law of conservation of momentum • States the total momentum of a group of objects stays the same unless outside forces act on the objects.