Notes – Chapter 4 – Forces in One Dimension

Force Force - Any push or pull acting on an object F = vector notation for the magnitude and direction F = only size of force Measured in : Newtons (N)

Force - Systems System – Objects or objects of interest External world – Everything around the system with which the system can interact. – hand, Earth, string, table, etc.

Forces Contact forces – When an object from the external world touches a system, exerting a force Field forces – Other ways in which the motion of objects can change. ie. gravity

Forces Contact forces – When an object from the external world touches a system, exerting a force Field forces – Other ways in which the motion of objects can change. ie. gravity

Fundamental Forces 1) Gravity – Causes an attraction between the mass of objects and produces weight 2) Electromagnetic - Causes an attraction between positive and negative charges 3) Nuclear – Strongest fundamental force. It holds protons and neutrons together in the nucleus of atoms

Forces - Agent Agent – The specific and identifiable cause of every contact and field force Eg. When you push your textbook, your hand (the agent) exerts a force on the textbook (the system) Contact forces – When an object from the external world touches a system, exerting a force Field forces – Other ways in which the motion of objects can change. ie. gravity

Free-body diagram

Net force Net force – The vector sum of all the forces on an object – Can be adding or subtracting

Net force

Laws of Motion Isaac Newton – 1686 – English scientist discovered the three laws of motion Motion – The change in position when compared to a reference point – Reference point – A place or object used to determine if something is in motion

2 nd Law: States that the acceleration of an object is proportional to the net force and inversely proportional to the mass of the object being accelerated a = F net _ m 2 nd Law of Motion

2 nd Law: States that the acceleration of an object is proportional to the net force and inversely proportional to the mass of the object being accelerated a = F net _ m 2 nd Law of Motion

2 nd Law: States that the acceleration of an object is proportional to the net force and inversely proportional to the mass of the object being accelerated a = F net _ m 2 nd Law of Motion

2 nd Law: States that the acceleration of an object is proportional to the net force and inversely proportional to the mass of the object being accelerated a = F net _ m 1 N= 1 kg x 1 m/s 2 = 1 kg- m/s 2 2 nd Law of Motion

Acceleration of an object depends on the amount of mass and the size of the force. Acceleration = change in speed or velocity over time. It could be speeding up, slowing down, or changing directions

2 nd Law of Motion Acceleration of an object depends on the amount of mass and the size of the force. Acceleration – change in speed or velocity over time. It could be speeding up, slowing down, or changing directions

The acceleration of an object is directly proportional to the force and inversely proportional to the mass a = F / m acceleration = Force / mass Large force = large acceleration Large mass = small acceleration 2 nd Law of Motion

The acceleration of an object is directly proportional to the force and inversely proportional to the mass a = F / m acceleration = Force / mass Large force = large acceleration Large mass = small acceleration 2 nd Law of Motion Large force + small mass = high acceleration small force + large mass = low acceleration Larger force = higher acceleration

Falling objects – All objects fall at the same rate Large mass small mass 2 nd Law of Motion Big Force little acceleration Little force big acceleration

Falling objects – All objects fall at the same rate Large mass small mass 2 nd Law of Motion Big Force little acceleration Little force big acceleration

1 st Law of Motion 1 st Law : An object that is at rest will remain at rest, and an object that is moving will continue to move in a straight line with a constant speed, if and only if the net force acting on that object is zero. 2 nd Law : if F net = 0, a = 0

1 st Law of Motion Law of Inertia. Inertia – Causes resistance to change in motion = Force? No : force= interactions of 2 objects – Friction – A force that slows down motion. – 1 st Law examples: It takes force to move an object. A hockey puck slides in a straight line across ice. Gravity keeps things stationary on Earth (stationary remains at rest)

1 st Law of Motion Law of Inertia. Inertia – Causes resistance to change in motion = Force? No – force= interactions of 2 objects – Friction – A force that slows down motion. – 1 st Law examples: It takes force to move an object. A hockey puck slides in a straight line across ice. Gravity keeps things stationary on Earth (stationary - remains at rest)

1 st Law of Motion Law of Inertia. Inertia – Causes resistance to change in motion – Friction – A force that slows down motion. – 1 st Law examples: It takes force to move an object. A hockey puck slides in a straight line across ice. Gravity keeps things stationary on earth(stationary - remains at rest) – Equilibrium : net Force = 0

1 st Law of Motion Law of Inertia. Inertia – Causes resistance to change in motion – Friction – A force that slows down motion. – 1 st Law examples: It takes force to move an object. A hockey puck slides in a straight line across ice. Gravity keeps things stationary on earth

Weight Weight = Gravitational force due to earth’s mass F g = mg g = gravitational field Earth’s surface = – 9.8 N/kg Apparent Weight = Gravity plus the support force acting on an object. – Elevator up = feel heavier – Elevator down = feel lighter

Weight Apparent Weight = Gravity plus the support force acting on an object. – Elevator up = feel heavier – Elevator down = feel lighter Weightlessness – No contact forces acting to support the object. Apparent weight = zero

Weight Apparent Weight = Gravity plus the support force acting on an object. – Elevator up = feel heavier – Elevator down = feel lighter Weightlessness – No contact forces acting to support the object. Apparent weight = zero

Drag force Drag force – Force exerted by a fluid on an object opposing motion through the fluid. – Depends on: motion of the object, properties of the object, properties of the fluid

Terminal velocity Terminal velocity – Constant velocity reached when drag force equals the force of gravity. – Light objects with large surface area = higher drag force – Heavy compact objects = lower drag force

Air resistance– Air friction slows down falling objects In a vacuum (no air) a feather would fall at the same rate as a bowling ball

Terminal velocity Terminal velocity – Constant velocity reached when drag force equals the force of gravity. – Light objects with large surface area = higher drag force – Heavy compact objects = lower drag force V terminal Tennis ball = 9 m/s Basketball = 20 m/s Baseball = 42 m/s Object shape influences drag force Fusiform – Egg shape – reduces drag Sky diver – Spread eagle = 60 m/s + parachute = 5 m/s

Terminal velocity Terminal velocity – Constant velocity reached when drag force equals the force of gravity. – Light objects with large surface area = higher drag force – Heavy compact objects = lower drag force V terminal Tennis ball = 9 m/s Basketball = 20 m/s Baseball = 42 m/s Object shape influences drag force Fusiform – Egg shape – reduces drag Sky diver – Spread eagle = 60 m/s + parachute = 5 m/s

Terminal velocity Terminal velocity – Constant velocity reached when drag force equals the force of gravity. – Light objects with large surface area = higher drag force – Heavy compact objects = lower drag force V terminal Tennis ball = 9 m/s Basketball = 20 m/s Baseball = 42 m/s Object shape influences drag force Fusiform – Egg shape – reduces drag Sky diver – Spread eagle = 60 m/s + parachute = 5 m/s

Terminal velocity Terminal velocity – Constant velocity reached when drag force equals the force of gravity. – Light objects with large surface area = higher drag force – Heavy compact objects = lower drag force V terminal Tennis ball = 9 m/s Basketball = 20 m/s Baseball = 42 m/s Object shape influences drag force Fusiform – Egg shape – reduces drag Sky diver – Spread eagle = 60 m/s + parachute = 5 m/s

Interaction Pairs – a set of two forces that are in opposite directions, have equal magnitude, and act on different objects F A on B = - F B on A The force of A on B is equal in magnitude and opposite in direction of the force of B on A 3 rd Law of Motion

Tension – The force that a string or rope exert. Tension equals the weight hanging force, or the pulling force from either side. 3 rd Law of Motion FTFT FgFg FAFA FBFB FAFA FBFB

Normal force – The perpendicular contact force that a surface exerts on another surface F N = mg F net = 0 3 rd Law of Motion

If one object exerts a force on another object, then the second object exerts a force of equal strength in the opposite direction. For every action (force) there is an equal and opposite reaction (force)

3 rd Law of Motion If one object exerts a force on another object, then the second object exerts a force of equal strength in the opposite direction. For every action (force) there is an equal and opposite reaction (force)

3 rd Law of Motion For every action (force) there is an equal and opposite reaction (force) Ex: Recoiling of a fired gun, a balloon travels in the opposite direction of air flow

3 rd Law of Motion Momentum - An object’s mass multiplied by its velocity Conservation of Momentum – When two or more objects collide, the total momentum of the object is the same after as before M 1 V 1 = M 2 V 2 1 kg x 10 m/s = 5 kg x ___ m/s

3 rd Law of Motion Conservation of Momentum – When two or more objects collide, the total momentum of the object is the same after as before Angular momentum – Velocity of rotation increases as the distance from the center becomes smaller

3 rd Law of Motion Conservation of Momentum – When two or more objects collide, the total momentum of the object is the same after as before Angular momentum – Velocity of rotation increases as the distance from the center becomes smaller