Forces and MotionForces and Motion

MotionMotionThe process of changing The process of changing from one position, or from one position, or place, to anotherplace, to another

PositionPositionObject’s place or Object’s place or locationlocation

Reference PointReference PointStationary object used to Stationary object used to determine the motion of determine the motion of another nearby objectanother nearby object

An object is moving if its An object is moving if its position changes compared position changes compared to a reference pointto a reference point

DistanceDistanceThe measure of how The measure of how far it is from one far it is from one point to another.point to another.

Speed:Speed:The distance an The distance an object travels object travels per unit of timeper unit of time

Formula for speed:Formula for speed:Speed = Speed = DistanceDistance

TimeTime

Question:Question:If a cyclist If a cyclist travels 45 travels 45 kilometers kilometers in 3 hours, in 3 hours, what is his what is his speed?speed?

Answer:Answer:Speed = 45/3 = Speed = 45/3 =

15 km/h15 km/h It is really important It is really important to include the units to include the units in your answer!!!in your answer!!!

F. Y. I.F. Y. I.Knowing the speed at which Knowing the speed at which something travels does not tell you something travels does not tell you everything about its motion. To everything about its motion. To describe an object’s motion describe an object’s motion completely, you need to know the completely, you need to know the directiondirection of its motion. For example, of its motion. For example, suppose you hear that a thunderstorm suppose you hear that a thunderstorm is traveling at a speed of 25 km/h. is traveling at a speed of 25 km/h. Should you prepare for the storm? Should you prepare for the storm? That depends on the direction of the That depends on the direction of the storm’s motion!storm’s motion!

Velocity:Velocity:Speed in a Speed in a given directiongiven direction

Symbols for MotionSymbols for MotionSymbolSymbol TermTerm

dd distancedistance

vv Velocity/speedVelocity/speed

tt timetime

Change (Delta)Change (Delta)

F. Y. I.F. Y. I. You know the You know the velocity of velocity of the storm the storm when you when you know that it know that it is moving 25 is moving 25 km/h km/h eastward.eastward.

What is a Force?What is a Force?

A force is a push or a A force is a push or a pull.pull.

Forces can…..Forces can…..Cause objects to moveCause objects to moveChange speedChange speedChange directionChange direction

For Example:For Example:A soccer player’s foot A soccer player’s foot touches a ball as he kicks touches a ball as he kicks it along the ground.it along the ground.

A student’s hand touches a A student’s hand touches a book as he lifts it out of a book as he lifts it out of a backpack.backpack.

Two Types of ForcesTwo Types of Forces

Balanced ForcesBalanced Forces

Unbalanced ForcesUnbalanced Forces

Balanced ForcesBalanced ForcesForces that cancel each Forces that cancel each other because they are other because they are equal in strength and equal in strength and opposite in directionopposite in direction

Examples of Balanced Forces:Examples of Balanced Forces:

A ball at rest on a soccer A ball at rest on a soccer field will not move until it field will not move until it is kicked.is kicked.

A chair will stay in place A chair will stay in place until it is pushed.until it is pushed.

Unbalanced ForcesUnbalanced Forces

Forces that do not cancel each Forces that do not cancel each other out and result in a change other out and result in a change in the speed or direction of the in the speed or direction of the motion of an object.motion of an object.

Example of Unbalanced ForceExample of Unbalanced ForceTug-of-WarTug-of-War

Two teams pull on a rope in Two teams pull on a rope in opposite directions. If one opposite directions. If one team pulls harder on the rope, team pulls harder on the rope, the forces are unbalanced.the forces are unbalanced.

Forces Acting – Direct ContactForces Acting – Direct ContactFriction can slow the motion of Friction can slow the motion of an object or keep an object from an object or keep an object from moving at all.moving at all.

Without friction, every surface Without friction, every surface would be more slippery, walking would be more slippery, walking would be impossible and you would be impossible and you would not be able to hold a would not be able to hold a pencil or write on paper.pencil or write on paper.

Forces Acting From a Distance Forces Acting From a Distance

Magnetic ForcesMagnetic ForcesElectrical ForcesElectrical ForcesGravity - A force that Gravity - A force that pulls objects toward pulls objects toward each othereach other

Question:Question:Would you be Would you be surprised if you let surprised if you let go of a pen you go of a pen you were holding and it were holding and it did not fall?did not fall?

F. Y. I.F. Y. I.One person who One person who put a great deal of put a great deal of thought into this thought into this question was Sir question was Sir Isaac Newton. He Isaac Newton. He concluded that a concluded that a force acts to pull force acts to pull objects straight objects straight down toward the down toward the center of the center of the Earth.Earth.

Example:Example:Newton realized that gravity acts Newton realized that gravity acts everywhere in the universe, not everywhere in the universe, not just on Earth. It is the force that just on Earth. It is the force that makes an apple fall to the makes an apple fall to the ground. It is the force that keeps ground. It is the force that keeps the moon orbiting around Earth. the moon orbiting around Earth. It is the force that keeps all of It is the force that keeps all of the planets in our solar system the planets in our solar system orbiting around the sun!!orbiting around the sun!!

Momentum:Momentum:A characteristic of A characteristic of a moving object a moving object that is related to that is related to how big the object how big the object is and how fast it’s is and how fast it’s movingmoving

F. Y. I.F. Y. I. The more momentum (the bigger The more momentum (the bigger it is and the faster it is moving) a it is and the faster it is moving) a moving object has, the harder it moving object has, the harder it is to stop. For example, you can is to stop. For example, you can catch a baseball moving 20 m/s, catch a baseball moving 20 m/s, but you cannot stop a car moving but you cannot stop a car moving at the 40 m/s. The car has more at the 40 m/s. The car has more momentum because it is bigger momentum because it is bigger and faster than the baseball!and faster than the baseball!

Newton’s First Law of MotionNewton’s First Law of Motionoror

The Law of Inertia The Law of InertiaAn object that is at rest will stay An object that is at rest will stay at rest until an unbalanced force at rest until an unbalanced force acts upon it. acts upon it.

For Example: Lurching forward For Example: Lurching forward in your seat as the bus you are in your seat as the bus you are riding in suddenly slowed downriding in suddenly slowed down

AccelerationAcceleration

The rate at which The rate at which velocity changesvelocity changes

Acceleration refers to:Acceleration refers to:

Increasing SpeedIncreasing SpeedDecreasing SpeedDecreasing SpeedChanging DirectionChanging Direction

Newton’s Second Law of MotionNewton’s Second Law of MotionAcceleration is produced when a force Acceleration is produced when a force acts on a mass. The greater the mass acts on a mass. The greater the mass (of the object being accelerated) the (of the object being accelerated) the greater the amount of force needed (to greater the amount of force needed (to accelerate the object). accelerate the object).

For Example: An empty grocery cart For Example: An empty grocery cart takes less force to push than a full takes less force to push than a full grocery cart. If your empty cart was grocery cart. If your empty cart was rolling down a hill, it would take much rolling down a hill, it would take much less force to stop it than a full grocery less force to stop it than a full grocery cart.cart.

Newton’s Third Law of MotionNewton’s Third Law of MotionFor every force there is an equal For every force there is an equal and opposite force. and opposite force.

For example, if you push on a For example, if you push on a wall, it will push back on you as wall, it will push back on you as hard as you are pushing on it. hard as you are pushing on it.