ENDURING UNDERSTANDINGSENDURING UNDERSTANDINGS

• A force is a push or pull in a given direction due to A force is a push or pull in a given direction due to applied energy.applied energy.

• Inertia is the tendency of an object to resist change Inertia is the tendency of an object to resist change in its motion.in its motion.

• Gravity is the force that pulls an object toward a Gravity is the force that pulls an object toward a rotating body. rotating body.

• Friction is the force that one surface exerts on Friction is the force that one surface exerts on another when the two rub against each other. another when the two rub against each other.

WHAT IS FORCE?WHAT IS FORCE?

• Force is a push or pull,Force is a push or pull,

described by its strength & directiondescribed by its strength & direction

• Force is measured in NewtonsForce is measured in Newtons

What forces do you see in this picture?What forces do you see in this picture?

1 N = 1 kg . m/s1 N = 1 kg . m/s22

UNBALANCED FORCESUNBALANCED FORCES

• Net force is the combination of all forces acting on an objectNet force is the combination of all forces acting on an object

• Unbalanced forces acting on an object result in a net force, Unbalanced forces acting on an object result in a net force, causing change in motioncausing change in motion

• Balanced forces in opposite directions result in no change in motionBalanced forces in opposite directions result in no change in motion

What forces do you see in this picture?What forces do you see in this picture?

Are the forces balanced or unbalanced?Are the forces balanced or unbalanced?

FRICTIONFRICTION• The strength of the force of friction depends on the types of The strength of the force of friction depends on the types of

surfaces involved and how hard the surfaces push together.surfaces involved and how hard the surfaces push together.

• Static friction is the force acting on objects that are not moving. Static friction is the force acting on objects that are not moving. Static friction must be overcome to begin moving an object.Static friction must be overcome to begin moving an object.

• Sliding friction occurs when solid surfaces slide over each other. Sliding friction occurs when solid surfaces slide over each other.

• Rolling friction occurs when an object rolls over another. Rolling friction occurs when an object rolls over another.

• Fluid friction occurs when an object moves through a fluid. The Fluid friction occurs when an object moves through a fluid. The force required to overcome fluid or rolling friction is much less force required to overcome fluid or rolling friction is much less than that required to overcome sliding friction.than that required to overcome sliding friction.

GRAVITYGRAVITY

• Gravity is the force that pulls an object toward a Gravity is the force that pulls an object toward a rotating body rotating body

• Newton’s Law of Universal Gravitation states "The Newton’s Law of Universal Gravitation states "The force of gravity acts between all objects in the force of gravity acts between all objects in the universe." universe."

MASS VS DISTANCEMASS VS DISTANCE

• Gravity between 2 objects depends on mass and distance. The Gravity between 2 objects depends on mass and distance. The greater the mass of a body, the stronger its force due to gravitygreater the mass of a body, the stronger its force due to gravity

The equation for the force of gravity between 2 objects is:The equation for the force of gravity between 2 objects is:

g = G g = G

where G is Einstein’s Universal Constant equaling 6.67 x 10 where G is Einstein’s Universal Constant equaling 6.67 x 10 -11 -11 N . kgN . kg22/m/m22

massmass11 x mass x mass22

rr22

Try it . . .Try it . . .A moon with a mass of 9 x 10A moon with a mass of 9 x 101515 N orbits a planet with a mass of N orbits a planet with a mass of

6 x 106 x 102727 N at a distance of 100,000 km. What is the force of N at a distance of 100,000 km. What is the force of gravity between the 2 bodies?gravity between the 2 bodies?

g = G g = G

mm11 x m x m22

rr22

9x109x101515 kg . 6x10 kg . 6x1027 27 kgkg

(100,000 km)(100,000 km)22g =g = 6.67 x 106.67 x 10-11-11 N . N . mm22

kgkg22

g =g =6.67 x 106.67 x 10-11-11 N . 5.4 x 10 N . 5.4 x 104343

1.0 x 101.0 x 1016 16 6.67 x 106.67 x 10-11-11 N . 5.4 x 10 N . 5.4 x 102727g =g =

3.6018 x 103.6018 x 1017 17 NNg =g =

6.67 x 10 6.67 x 10 -11-11 N . N .

g =g =54 x 1054 x 104242 kg kg22

(100,000,000 m)(100,000,000 m)22

mm22

kgkg22

FREE FALLFREE FALL

• When the only force acting on a falling object is When the only force acting on a falling object is gravity, it is said to be in free fall gravity, it is said to be in free fall

• In free fall, the force of gravity is an unbalanced In free fall, the force of gravity is an unbalanced force that causes objects to accelerateforce that causes objects to accelerate

• The force of acceleration due to gravity on Earth The force of acceleration due to gravity on Earth is 9.8 m/sis 9.8 m/s22

GRAPHING GRAVITYGRAPHING GRAVITY

• Acceleration due to gravity is Acceleration due to gravity is plotted on a speed versus time plotted on a speed versus time graphgraph

AIR RESISTANCEAIR RESISTANCE

• Air resistance is a type of fluid friction that falling objects Air resistance is a type of fluid friction that falling objects experience. experience.

• Air resistance is an upward force, opposite of gravity. Air resistance is an upward force, opposite of gravity.

• Air resistance increases as velocity increases.Air resistance increases as velocity increases.

• Terminal velocity is the greatest velocity that an object Terminal velocity is the greatest velocity that an object reaches; such as when air resistance equals the force of reaches; such as when air resistance equals the force of gravity on a falling object, so although the object continues to gravity on a falling object, so although the object continues to fall, it is no longer accelerating.fall, it is no longer accelerating.

FALLING MOTIONFALLING MOTION• In the absence of friction, all In the absence of friction, all

objects free fall at the same objects free fall at the same rate regardless of massrate regardless of mass

• A projectile falls at the same A projectile falls at the same rate as an object in free fallrate as an object in free fall

NEWTON’S LAWSNEWTON’S LAWS• Newton’s First Law - Inertia is the tendency of an object to Newton’s First Law - Inertia is the tendency of an object to

resist change in motionresist change in motion

• Newton’s Second Newton’s Second Law – Force equals Law – Force equals mass times mass times accelerationacceleration

NEWTON’S THIRD LAWNEWTON’S THIRD LAW

• If an object exerts a force on If an object exerts a force on another object, the second another object, the second object exerts a force of equal object exerts a force of equal strength in the opposite strength in the opposite directiondirection

• In other words, for every action In other words, for every action there is an equal and opposite there is an equal and opposite reactionreaction

MOMENTUMMOMENTUM

• Momentum deals with an object's inertia. The higher the Momentum deals with an object's inertia. The higher the velocity and mass, the more momentum an object has. velocity and mass, the more momentum an object has.

Momentum = mass X velocityMomentum = mass X velocity measured in measured in kg * m/skg * m/s

• The Law of Conservation of Momentum states “The total momentum of any group of objects remains the same unless outside forces act on the objects.” When 2 objects collide in the absence of friction, momentum is not lost.

When a fast-moving object hits a slower moving object traveling When a fast-moving object hits a slower moving object traveling in the same direction, the slower moving object will accelerate in the same direction, the slower moving object will accelerate to the speed of the fast-moving object, and the fast- moving to the speed of the fast-moving object, and the fast- moving object will slow to the speed of the slower moving object. object will slow to the speed of the slower moving object.

No momentum is lost, except to friction.No momentum is lost, except to friction.

Momentum of 2 Moving ObjectsMomentum of 2 Moving Objects

MOMENTUM OF 1 MOVING OBJECTMOMENTUM OF 1 MOVING OBJECT

When a moving object hits a stopped object its motion transfers to When a moving object hits a stopped object its motion transfers to the stopped object, and the first moving object will stop moving.the stopped object, and the first moving object will stop moving.

Momentum of 2 Connected ObjectsMomentum of 2 Connected Objects

If a moving object hits and connects with a stopped object, half If a moving object hits and connects with a stopped object, half of its momentum transfers to the other object and they travel of its momentum transfers to the other object and they travel together with twice the mass but half the velocity, so total together with twice the mass but half the velocity, so total momentum is conserved.momentum is conserved.

CENTRIPETAL FORCECENTRIPETAL FORCE

• Centripetal Force is a balance between the force of gravity of Centripetal Force is a balance between the force of gravity of one object and the inertia of the other; or a force that causes one object and the inertia of the other; or a force that causes an object to move in a circle, as one body orbiting another an object to move in a circle, as one body orbiting another

Try it . . .Try it . . .• What is force? How is it described? What units represent force?What is force? How is it described? What units represent force?

• What is inertia?What is inertia?

• What is net force?What is net force?

• Compare / contrast balanced with unbalanced forces.Compare / contrast balanced with unbalanced forces.

• What is friction? Describe the 4 types of friction.What is friction? Describe the 4 types of friction.

• What is gravity? Describe Newton’s Law of Universal Gravitation.What is gravity? Describe Newton’s Law of Universal Gravitation.

• What is the equation for gravitational force between 2 objects?What is the equation for gravitational force between 2 objects?

• What is Einstein’s gravitational constant?What is Einstein’s gravitational constant?

• What is free fall? What is the acceleration due to gravity on Earth?What is free fall? What is the acceleration due to gravity on Earth?

• What is air resistance? How does it create a terminal velocity?What is air resistance? How does it create a terminal velocity?

• Describe projectile motion.Describe projectile motion.

• Describe Newton’s First, Second & Third Laws. Describe Newton’s First, Second & Third Laws.

• What is momentum. Describe the Law of Conservation of Momentum.What is momentum. Describe the Law of Conservation of Momentum.

• Describe the motions of 1 moving object, 2 moving objects & 2 connected Describe the motions of 1 moving object, 2 moving objects & 2 connected moving objects.moving objects.

• Describe centripetal force.Describe centripetal force.