Chapter 12 Forces and Motion Part 1 Newton’s First Law of Motion

What is motion? Motion: An object moving at a speed greater than zero in a given direction. Motion is caused by an outside force  A force is a push or pull

Aristotle’s Classification of Motion Motion requires a force Natural Motion- objects have resting places they naturally seek; natural for heavy object to fall faster than light ones Unnatural Motion- motion that requires forces imposed by people or animals

Galileo’s Concept of Inertia Galileo disproved the idea that heavy objects fall faster than light objects- he used experiment! A force is required to start an object moving, but no force is required to keep it moving Inertia- the tendency of an object to remain as is; objects at rest will stay at rest

Speed and Velocity Speed- the rate of change of position (the distance traveled in a given time) Speed= Distance/Time Velocity- the speed of an object and the direction of its motion (how fast AND in what direction!) Ex. 45m/s west

Velocity Constant speed= steady speed Constant Direction is a straight line Constant velocity= constant speed AND constant direction 44m/s east

Motion is Relative Everything is always moving When discussing motion, we mean relative to something else You are walking down the aisle of a train at 1m/s. What is your speed relative to the floor of the train? What is your speed relative to the ground if the train is moving 50m/s?

Sir Isaac Newton Newton is one of the greatest scientists of all time  Grew up on a farm then attended Cambridge University  Invented Calculus, formulated and proved the universal law of gravitation, laws about motion, developed a theory of the nature of light  Wrote 2 very important books

Newton’s 1 st Law: Law of Inertia Built on Galileo’s findings. Every object continues in a state of rest, or state of motion in a straight line at constant speed, unless it is compelled to change that state by forces exerted upon it. An object moves by its own inertia.

Net Force- Combination of All Forces that Act on an Object Without force objects do not speed up, slow down, or change direction Net Force= sum of all forces acting on an object Newton (N)- scientific unit for force

Arrows Vector Quantity- direction and magnitude Velocity and other forces are shown with arrows  The direction the arrow points is the direction of the force  The size of the arrow represents magnitude (how much) of force So a small arrow means a small force in that direction Draw a picture of you standing on the floor and draw the force of gravity

Interacting Forces More than one force can act on an object The sum of these forces is the net force Remember: arrows show the direction of the force Add arrows pointing in the same direction Subtract arrows pointing in opposite directions When the net force on an object is zero, it is said to be in equilibrium

What is Equilibrium? Tension is a stretching force and can be measured using a weighing scale Newtons (N), like pounds, are units of weight and measure a force The Equilibrium Rule- when the net force acting on an object is zero, it is in equilibrium  F=0

The Support Force If the book on your desk is in equilibrium (all forces=0), what forces are acting on the book? Support Force- the upward force of a surface that keeps an object from falling

Equilibrium for Moving Objects An object is in equilibrium when: 1. It is not moving. 2. It is moving in a constant speed in a straight-line path (constant velocity). 3. Two or more forces are acting on it. 4. The forces on it add up to zero.

Forms of Equilibrium Objects at rest are in static equilibrium, Objects moving at constant velocity are in dynamic equilibrium. *Equilibrium is any state of no change.