Forces1DynamicsFORCEMAN

What causes things to move?ForcesWhat is a force?A push or a pull that one body exerts on another.2

Balanced3No change in motion

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UnbalancedIf the forces acting on a body are "unbalanced" this means that there is a "net" or "resultant" force.The body will do one of the following:Speed UpSlow DownChange the Direction of its MotionIn other wordsThe Body will Accelerate

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NewtonsSI unit of force is the Newton (N).Defined as the amount of force that when acting on a 1 kg object produces an acceleration of 1m/s2. Therefore, 1N = 1 kg m s27

Newtons First Law8

9Newtons First Law

Newtons First Law An object at rest stays at rest, and an object in motion stays in motion unless acted upon by a net external force.What do you mean by Net Force?Net means: Final Sum, so net external force is the sum of all the forces acting on the object.10

Newtons First Law Inertia is the tendency of an object to resist any change in its motion.Newtons First Law is also called the Law of Inertia.11

Why does the ladder continue to move?Inertia!12

Why does the person continue to move?

Inertia!Clip13

Newtons Second LawThe acceleration of an object is directly proportional to the net external force acting on the object and inversely proportional to the objects mass.F=maClip14

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Force = mass x acceleration

Newton's 2nd Law of Motion: Mass is in kg Acceleration is in m/s2 Force is in kg x m/ s2 (or N) F = (ma)16

Force Problems:What force is needed to give an object with a mass of 25.0 kg an acceleration of 15.0 m/s2 ?

Given:Unknown:m = 25.0 kga = 15.0 m/secF = ?FormulaF = maF = (25 kg)(15 m/sec)F = 375 kgm/sec = 375 N17

Newtons Third Law"Every action has an equal and opposite reaction."

Newtons Third Law of Motion34to every action force there is an equal and opposite reaction force

35Action-Reaction forces act on different objects

36Review Newtons Laws Clip

Forces that oppose motion18

19-Friction is a force that opposes motion between two surfaces that are touching each other. Forces that oppose motionFriction Song 2Friction Song 1

-Air resistance is the force air exerts on a moving objectForces that oppose motion

Friction

What Causes Friction?Microscopic, electrostatic interactions between contacting surfacesThree types of friction:Static FrictionSliding FrictionRolling Friction

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Types of FrictionTypes of friction: 1. Static force required to overcome inertia of a stationary object 21

Static Friction (FS)22

To decrease friction, surfaces can be lubricated with a liquid such as oil.3. Rolling force required to keep an object rolling at a constant speed 2. Sliding force required to keep an object sliding at a constant speedTypes of Friction (cont.)23

FRICTION LAB

CLIP The amount of force required to overcome static friction is always greater than the force required to overcome sliding or rolling friction.24

GRAVITY!! The force of gravity is an attractive force between objects. The amount of GRAVITATIONAL FORCE between objects depends upon their:1- Masses (greater mass means more gravity)2- Distance apart (greater distance means less gravity) *All objects fall toward the earth at the same rate of acceleration, regardless of their masses!25

Calculating the Gravitational Force26

27Gravitation

Weightlessness Gravity in Space28MoonMoon Hammer & Feather

Free fall and Terminal VelocityThe opposing force of air resistance increases with speed.Objects accelerate towards the Earth until the force of gravity is cancelled or balanced by this air resistance.This is the highest speed an object can reach.Different objects have different terminal velocities.29

Weight and Gravity30Weight is the force of gravity between the earth and a body on its surface.Weight mass!Weight is measured in Newtons (N). BECAUSE ITS A FORCE!W =m x g

Could your weight change by simply going to the top of a mountain?31

WeightWhen the mass of an object and the acceleration due to gravity are known, the weight of an object can be calculated.32Ex. Mass = 100kg Acc.= 9.81 m/s2Weight = 981 NW = (g)(m)

Example ProblemWhat is your weight if your mass 4.52 kilograms?Given:Unknown:m = 4.52 kgW = ?g = a = 9.8 m/sec

Formula: W = mg W = (4.52kg)(9.8 m/sec)W = 44.296 kgm/sec = 44.296 N33

Projectile MotionProjectiles follow a curved path because of the Earths gravitational pull. They have 2 types of motion that are independent of each other:1. Horizontal motion2. Vertical motion 37

Projectile MotionWhich will hit the ground first?A ball that is dropped straight down or a ball that is shot out horizontally?* An object launched horizontally will land on the ground at the same time as an object simply dropped from the same height!!!!38

Another Example of Projectile Motion39

Circular Motion An object moving in a circular motion at the same speed is accelerating toward the center because its direction is constantly changing. Centripetal acceleration is acceleration toward the center of a curved path.40'Centripetal' comes from the Latin word for 'center seeking' only centripetal is the real force Centrifugal 'force' is really a function of the inertia of the object being pushed into a circle. It is not really a force at all, it is simply the tendency of an object to go in a straight line. Roller Coaster Clip

Circular Motion cont. Centripetal force is the force that causes a moving object to move in a curved pathWithout a centripetal force, an object in motion continues along a straight-line path.With a centripetal force, an object in motion will be accelerated and change its direction.41

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How do rollercoasters work!?!Amusement Park Forces43