Chapter 23 Section 2

Transcription

1 Chapter 23 Section 2

2 Title: Vocabulary Activity Chapter 23 Section 2 Copy from the textbook the definitions of the following words: Force Contact force Long-range force Inertia Newton s First law of Motion Balanced forces Unbalanced forces

3 FORCE Force is a push or a pull from one object on another. **SI unit = Newton (N) A force has a magnitude and a direction

4 There are two types of force: Contact Force and Long range force

5 Contact Force Contact Force is a force that involves objects touching each other EX: a mother pushing a stroller

6 Long Range Force are forces that act on objects without direct contact. Long Range Force Ex: Gravity objects in free fall Magnetism magnets pull or push on each other also if they are not touching Fig 7 page 691

7 How do objects move???? Objects move because there are forces being applied to them ****Net Force Is the combination of all forces acting upon an object If the net force is zero: what is happening to the object???????? (two options)

8 How do objects move???? Net Force ****If the combination of forces is ZERO two things could happen: A) if the object is moving, this object will continue moving at the same speed B) if the object is at rest, the object will continue at rest

9 If the net force is not zero, the object will move in the direction of the stronger force

10 How do objects move???? There are different forces that will act upon objects to make them move: Balanced forces Unbalanced forces

11 Balanced Forces 1) Balanced forces are always equal in magnitude (strength) 2) They act in opposite directions and cancel each other. THE NET FORCE IS ALWAYS ZERO

12 Balanced Forces REMEMBER: IF THE NET FORCE IS ZERO there will not be a change in the motion. An object in motion will stay in motion An object at rest will stay at rest Net force will not change the motion of an object

13 1) Unbalanced forces will cause a change in the motion of an object. Unbalanced forces 2) The forces can be in the opposite or in the same direction 3) The forces have different magnitudes. NET FORCE IS NOT ZERO.

14 Unbalanced forces (net force different than zero) What is the net force in the picture below? In which direction will the car move?

15 Example What is the Net Force being applied to the rope? Who is going to win? Net Force = 20 N to the left

16 LAWS OF MOTION

17 Once upon a time. There was a British man called Isaac Newton, who lived during the 17 th century

18 Newton was part of the nobility, so he had plenty of time to observe the world around him. History tells, that Isaac loved apples Who knows what happened to Isaac?

19 One day he was sitting under an apple tree and an apple fell on his head.. Because of that apple, he discovered the force of Gravity. He also developed 3 laws to explain MOTION

20 Newton described 3 laws that explain MOTION

21 Newton s First Law of Motion or Law of Inertia or Seatbelt law What happens to your body when the car comes to a stop, unexpectedly????? Your body tends to continue in motion What happens to your body when the car starts moving????? Your body tends to stay at rest This is what the First law states!

22 Newton s First Law of Motion or Law of Inertia or Seat Belt law *An object at rest tends to stay at rest and an object in motion tends to stay in motion UNLESS acted upon by a force.

23 Connecting Concepts Sections 1 and 2 **** Motion X Force A force is needed to change an object s motion. To accelerate an object we need to apply a force that: will speed up slow down or change the direction of an object

24 There are 2 forces involved in Motion: Inertia and Friction **Inertia: tendency of an object to resist a change in motion (person in a car tends to continue moving also if the car stops!) **It depends on the mass *** The more mass, the more inertia What is easier to stop: a mouse or an elephant? It is easier to stop an mouse in motion than an elephant in motion, because the mouse has less mass.

25 There are 2 forces involved in Motion: Inertia and Friction *Friction: it is a force that resists the motion of two surfaces rubbing against each other. It is a contact force. In which direction, compared to the motion, is the force of friction exerted? **Friction is a force that is applied in the opposite direction of the motion