Chapter 23 – Section 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

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

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

Contact Force

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

Long Range Force

⚫Long Range Force – are forces that act on objects without direct contact.⚫Ex:

Gravity – objects in free fall Magnetism – magnets pull or push on each other also if they are not touchingFig 7 page 691

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)

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

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

How do objects move????

There are different forces that will act upon objects to make them move:⚫Balanced forces⚫Unbalanced forces

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

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

Unbalanced forces

1) Unbalanced forces will cause a change in the motion of an object.

2) The forces can be in the opposite or in the same direction3) The forces have different magnitudes.NET FORCE IS NOT ZERO.

Unbalanced forces(net force different than zero)

⚫What is the net force in the picture below? ⚫In which direction will the car move?

Example

What is the Net Force being applied to the rope?Who is going to win ?

Net Force = 20 N to the left

⚫LAWS OF MOTION

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

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?

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

Newton described 3 laws that explain MOTION

Newton’s First Law of Motion or Law of InertiaorSeatbelt 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!

Newton’s First Law of Motion or Law of InertiaorSeat 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.

Connecting ConceptsSections 1 and 2

**** Motion X ForceA 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

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.

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