What is a force? Pick up 2 sheets in the back

Watch the book Watch the book What am I doing in all of these demonstrations? What am I doing in all of these demonstrations? I am applying a force Definition of FORCE Definition of FORCE Any push or pull that causes an object to change its current state of motion or shape

Can forces be seen? No– only the result of the application of the force can be seen. Watch the ball: You can’t see the force I apply to the ball. You can only see the result of the force the ball moves

What is the unit of force? What is the unit of force? A Newton- named after Sir Isaac Newton Abbreviation – capital N What does it mean? A force of 1 N gives an acceleration of 1 m/s/s to a 1kg mass.

Forces can be used to change the state of motion of an object or change the shape of the object. Forces can be used to change the state of motion of an object or change the shape of the object. Can start objects moving Can stop moving objects Can change the direction of an object’s motion Can change the shape of an object Can change the shape of an object Crumpling a piece of paper Crumpling a piece of paper Forces can result in ACCELERATIONS

Sometimes you can exert a force on an object and no change in motion or shape occurs. Sometimes you can exert a force on an object and no change in motion or shape occurs. These types of forces are called. These types of forces are called. balanced forces Definition of balanced force: Definition of balanced force: A force that produces no change. A force that has an equal and opposing force. Equal in size and opposite in direction

Example: A person sitting in a chair. (Force arrow diagram) Example: A person sitting in a chair. (Force arrow diagram) 100 N

Arrows symbolize forces. These arrows have both size (scientists call it magnitude) and direction. Therefore, force is a vector quantity. Arrows symbolize forces. These arrows have both size (scientists call it magnitude) and direction. Therefore, force is a vector quantity. The forces we spoke of earlier, the ones that changed the state of motion of an object or the shape of the object are called. This is the type of force needed to produce motion. The forces we spoke of earlier, the ones that changed the state of motion of an object or the shape of the object are called UNBALANCED FORCES. This is the type of force needed to produce motion.

Example : A person who breaks a chair by sitting on it. Example : A person who breaks a chair by sitting on it.

Unbalanced forces produce a net force. A net force causes a change in the current state of motion of an object. It can also cause the shape of an object to change. Unbalanced forces produce a net force. A net force causes a change in the current state of motion of an object. It can also cause the shape of an object to change. Example: Tug of war (Force arrow diagram) Example: Tug of war (Force arrow diagram) Net force = 5 N to the left

Before we go any further we need to talk about types of forces. There are many types of forces but we will only touch on seven in detail. There are two others I’d like to mention: Before we go any further we need to talk about types of forces. There are many types of forces but we will only touch on seven in detail. There are two others I’d like to mention: Nuclear force: The strong nuclear force is the force that holds the protons and neutrons together in the nucleus of atoms. Nuclear force: The strong nuclear force is the force that holds the protons and neutrons together in the nucleus of atoms. Molecular force: The attraction of molecules for each other results in two kinds of forces. Molecular force: The attraction of molecules for each other results in two kinds of forces. Cohesion-force of attraction between like molecules (ever do a belly flop?) Cohesion-force of attraction between like molecules (ever do a belly flop?) Adhesion-force of attraction between unlike molecules (tape, glue-adhesives) Adhesion-force of attraction between unlike molecules (tape, glue-adhesives)

Applied Force

Gravity Force “weight”

Normal Force Balanced forces- no change in current state of motion

Frictional Force Friction opposes motion Must be contact between two surfaces

Air Resistance Unbalanced forces object accelerates

Air Resistance #2 Piece of paper falling to the ground Balanced forces Object falls at a constant speed

Tensional Force Teachers Win!

Spring Force Mass hanging on spring Stretched spring Spring wants to return to rest position

Spring Force #2 Compressed Spring Spring wants to return to rest position

Divide the front side into 6 equal boxes Divide the back into 4 boxes Divide the back into 4 boxes Create the 10 diagrams for homework. Create the 10 diagrams for homework. Follow the directions Follow the directions Read the descriptions carefully. Read the descriptions carefully. Free Body Diagrams