Chapter 3.2 & 3.3 Forces and Energy!!

Force Force is a push or a pull on an object! Forces can change the shape or motion of an object!

Force Lets recap! What is acceleration? It is a change in motion!!! What causes acceleration? It is caused by a Force!

Types of Forces! Frictional Force This is a force that opposes motion.

Types of Forces! Gravitational Force Gravity is a force that all objects exert on each other. Newton’s Law of Universal Gravity states that all objects in the universe will attract other object with a force known as gravity!

Types of Forces! The unit of the measurement of gravity (weight) is the Newton (N). In the US we use the pound. The relationship between the masses of objects and the pull they have is directly related to the size of the mass! A bigger mass (like a star) has more gravity than a pencil!

Types of Forces Gravity is also inversely related to the square of the distance between the two objects. In other words…the farther apart they are, the less the force of gravity.

Newton’s Laws of Motion In order to understand Newton’s laws of motion, we first have to understand “Inertia”. Inertia is a property of matter whereby all matter resists change in its motion! If an object is at rest, it “wants” to remain at rest. If an object is in motion, it “wants” to remain moving!

Inertia For example: A football will sit until it is thrown or kicked. Once thrown or kicked, the football will keep moving until something (like the ground) stops it! Forces are the agents causing changes in motion.

Newton’s First Law of Motion The first law of motion is based on the principle of inertia: the velocity of an object is not changed unless acted on by an outside force. This principle is equally true of objects in motion and objects at rest.

Newton’s Second Law of Motion This second states that an object accelerates in the direction of the applied force. It also states that the acceleration is directly related to the force and inversely related to the mass. There is an equation that shows this relationship: a = F/m or F = ma

Newton’s Third Law of Motion The third law states that: For every action there is an equal and opposite reaction. In other words, forces come in pairs… Push on a wall, it pushes back on you… Push on a basketball, it pushes back on you!

Newton’s Third Law of Motion Action/Reaction is why rockets get lift as they thrust off the ground.

Solids in a Circular Motion Objects move in a circular path. When an object swings around from a fixed string, the direction of the motion keeps changing. This pull keeps the weight from moving in a straight line. This is a force called centripetal force.

Centripetal Force The word centripetal means “to seek center” It is a force that causes an object to move in a curved path rather than a straight path.

Centrifugal Force Centrifugal force is the force that acts in the opposite direction of the pull on the object. It is the pull of the object on the fixed location of the string. Without centripetal force, centrifugal force cannot exist.

Gravity Gravity is a centripetal force that keeps the planets from continuing in a straight path away from the sun.

Energy for Movement Energy in the scientific sense is the ability to do work. Work is only done when a force is applied and an object moves in the direction of the force applied. We can experience and observe the effects of energy on matter and hear sound energy.

Mechanical Energy Matter in motion or with potential of motion possesses Mechanical Energy. Energy is always conserved!!! Energy changes form from one type of energy to another, but it is never “LOST”.

Mechanical Energy There are many types of energy!!! – Electrical Energy – Chemical Energy – Heat Energy – Sound Energy – Nuclear energy – These are just some!!!

Energy of Motion!! Mechanical Energy can be classified as either Kinetic or Potential. Kinetic Energy is Energy in Motion Potential Energy is Energy of Position, or Condition, or it is known as Stored Energy!

Tackle This!!! Turn to page 118 in your books! Answer the Tackle This Questions!!! You can answer this next to your page of notes!