PATTERNS OF MOTION AND EQUILIBRIUM

Galileo`s concept of inertia • Force: is a push or pull. It is

needed to start an object moving. No force is needed when it starts moving, just the force to overcome friction.

• Inertia: the property of things to resist changes in motion. So a ball moving horizontally would move forever if friction is totally absent.

Concept of inertia

Concept of inertia • Every material object

possesses inertia: how much depends on its amount of matter. The much matter, the much inertia (that means it has more mass)

• When comparing 2 objects, you should compare the abilities to be resistant to a change in motion.

Mass vs Weight • Mass: quatity of matter in an

object. It`s a measure of inertia that an object exhibits in response to any effort made to start it, stop it, or change its state of motion in any way. (SI Unit: Kilogram)

• Weight: force upon an object due to gravity. (SI Unit: Newton) W=m x g

• Directly proportional to each other. • Gravitation force: 9.8N• 1 Kg= 9.8N

Vectors and scalars• Vector quantity: directed

quantity. It has to be specified not only by magnitude (size) but by direction as well. May be represented by arrows Ex: velocity

• Scalar quantity: can be specified by magnitude alone. Ex: speed

Adding vectors

• Vectors that are add together are called component vectors. The sum of component vectors are called a resultant.

• DO NOT MIX VECTORS!!!!!

Net force• Objects don`t speed up, slow down or change

direction unless a force acts.• The NET FORCE is the total force acting on an

object. A combination of forces that changes an object`s state of motion.

• It is a vector quantity, arrows represented the direction of the quantity.

The equilibrium rule

• Forces are balanced

• There`s no motion

• Called mechanical equilibrium

Support force

• Called NORMAL force

• The force that supports an object against gravity

Dynamic equilibrium

• STATIC equilibrium: when an object is NOT moving

• DYNAMIC equilibrium: once in motion, if there is no net force to change the state of motion, it moves at an unchanging speed.

∑F= 0

Force of friction• Resistive force that opposes the motion or

attempted motion of an object past another with which it is in contact.

• For solids, liquids and gases

• ALWAYS in opposite direction to motion

• Ex: air resistance

Force of friction

• Depends on: the kind of material and how much surfaces are pressed together

Types of Friction

• Dry friction:

- Static friction: the object has no motion.

- Sliding friction: the object moves.

• Lubricated friction: Needs a lubricant to start moving.

• Fluid friction: resistance in liquids.

• Air resistance: resistance of an object to move in the air.

Instantaneous speed

• The speed at any instant

• Most of the time, it is different than the average speed

Velocity• Constant velocity means constant speed and

direction• Direction in a straight line: no curves• No change in velocity, means no acceleration• Works with displacement (net distance)

Motion is relative

• Everything is always moving

• Motion is relative to different objects

Acceleration• Variation is motion, in velocity

Average acceleration

Acceleration• Recognizing Acceleration on a Graph

Acceleration can be shown on a graph of velocity versus time.

Tracks• Circular Motion: Continuous Acceleration

An object traveling in a circular motion is always changing its direction. Therefore, its velocity is always changing, so it is accelerating.

• The acceleration that occurs in circular motion is known as centripetal acceleration.

Tracks

• Linear motion: motion along a straight line.

• It can be uniform, with constant speed or non uniform with a variable speed

• An example of linear motion is that of a ball thrown straight up and falling back straight down.

• objects not subjected to forces will continue to move uniformly in a straight line indefinitely

Tracks

• Parabolic motion: A projectile is an object upon which the only force is gravity. Gravity, being a downward force, causes a projectile to accelerate in the downward direction.