Force and Motion 2011

First we need to define the word FORCE: A push or pull resulting from the interaction of two objects. Two types of forces Pushes Pulls

Describing Forces Forces can be described by… The size of the force, known as magnitude The direction of the force Both factors can be represented by an arrow, known as a VECTOR.

Measuring Forces Forces are measured in Newtons SI unit of force Symbol: N Measured by using a spring scale

Forces may be balanced or unbalanced Balanced forces – all forces acting on an object are equal There is NO MOTION Unbalanced forces – one or more forces acting on an object are stronger than others There is MOTION Net Force is the combination or total of all forces acting on an object

Calculating Net Force Net Force = 2 N right Net Force = 10 N right When forces act in the SAME DIRECTION, you must ADD the forces to determine the net force. When forces act in OPPOSITE DIRECTIONS, you must SUBTRACT the forces to determine the net force.

Newton’s Laws and Forces First Law – Inertia, Unbalanced/Balanced, Friction Second Law – Acceleration, Force & Mass Third Law – Action-Reaction

What is Friction? Friction force that opposes the motion of an object the force of friction works in the opposite direction of the force of motion Friction slows things down

Types of Friction Sliding Kinetic Friction Rolling Kinetic Friction the source of friction is the contact between two surfaces, at least one of which is in motion Rolling Kinetic Friction friction between two surfaces that are not in constant contact ex. Wheels Static Friction When a force is applied to an object but that force does not cause the object to move Air Resistance friction results from air pushing on an object as it is moving

Harmful vs. Helpful Friction Friction can be both harmful and helpful to us in our everyday lives. HARMFUL FRICTION HELPFUL FRICTION Holes in your socks or jeans Paper and pencil to write Erosion of topsoil Walking without slipping Worn/rusted car parts Brakes on a car Sliding on a banana peel Moving furniture

Ways to Reduce/Increase Friction Use of Lubricants such as oil, wax, or grease Make surfaces smoother Switch from sliding to rolling kinetic friction Increase the amount of force being applied

What is motion? When an object’s distance changes relative to a reference point.

What is a reference point? An object used for comparison to see if something is in motion!

So….How do you know that you are moving? It depends on how you look at things. You can use different reference points to justify the motion of the same object. Look at the books on your table. Are they moving? Use the floor as a reference point. What if the sun is your reference point?

More examples…. Explain how the illustrations are examples of motion and no motion.

Speed The distance traveled divided by the time taken to travel that distance Speed = Distance ÷ Time

Units for Speed…. Units for speed will be unit of distance over a unit of time (miles per hour or meters per second) Units for distance are (millimeters, centimeters, kilometers etc.) Units for time will be (seconds, minutes, hours etc.)

SPEED IN A GIVEN DIRECTION! WHAT IS VELOCITY? SPEED IN A GIVEN DIRECTION! Example: The Atlanta Falcons are traveling to Miami to play the Dolphins. The team bus travels at 90km/hr. What is the velocity of the bus?

WHAT IS ACCELERATION? When an object does ANY of the following, it is called acceleration… Speeds up Slows Down (deceleration) Changes Direction Calculating Acceleration (Final Velocity – Original Velocity )÷ Time

What is Gravity? Gravity is force of attraction between all objects in the universe

Law of Universal Gravitation All objects in the universe attract each other through gravitational force. The size of the force depends on an objects Mass Distance between the objects

Gravity is affected by distance the greater the distance between two objects, the smaller the gravitational force Increased force of gravity Decreased force of gravity

Gravity is affected by mass the larger an object’s mass, the greater the gravitational force Not much gravity More gravity Lots of gravity

Air Resistance Air resistance is the force that opposes the motion of objects through air. The amount of air resistance acting on an object depends on: The size of the object The shape of the object The speed of the object