KD3 Linear Mechanics Chapters 4, 5 & 6

Force Force- A push or pull which can change an object’s state of rest or motion (if the force is unbalanced) – Measured in Newtons (N)

Force is measured in Newtons Newton-force that causes a mass of 1 kg to accelerate at a rate of 1.0 m/s ² 1 N =.225 lb or 1 lb = 4.45 N

4 Types of Force 1. Gravitational Force-An attractive force that exists between all objects – Ex) Earth and the Moon 2. Electromagnetic Force-The force involved in electric and magnetic fields – Ex) Friction

4 Types of Forces Cont.. Strong Nuclear Force-Holds particles in the nucleus together Weak Force-A form of electromagnetic force involved in the radio active decay of some nuclei

Newton’s First La w (Law of Inertia) An object at rest stays at rest, an object in motion stays in motion unless acted on by an unbalanced force

Inertia Inertia - objects resistance to a change in motion – NOT a force! – All objects have inertia – More massive objects have more inertia than less massive objects

Newton’s 2 nd Law The acceleration of a body is directly proportional to the net force on it and inversely proportional to the mass F = m a

Newton’s 2 nd Law

Mass vs. Weight Mass-The amount of matter “stuff” from which a body is made – Measured in kg – Never changes regardless of gravity (can change if removed)

Mass vs. Weight Weight- Mass times the acceleration due to gravity – Measured in N (kg m/s ² ) – Refers to the gravitational force exerted by a large body (Ex. Earth) on an object – Varies depending on where you are (elevation, different planet)

Weight Weight is a force Measured in Newtons Force = wt = m g

Example A person with a mass of 50 kg has what weight on Earth? Wt. = m g Wt. = 50 kg (9.8 m/s 2 ) Wt. = 500 N

Example A person weighting 160 lbs, has a mass of what? (1 lb = 4.45 N)

Law of Universal Gravitation A force of attraction (gravity) exists between any 2 objects F = G m 1 m 2 r ² F = Force (N) G = 6.67 X Nm ² /kg ² m = mass (kg) r = distance (m)

Inverse Square Law The gravitational force between any 2 objects varies inversely to the square of the distance between them (more distance less attraction) The gravitational force between any 2 objects varies directly to the mass of the objects (more massive = more attractive)

Law of Universal Gravitation What happens to the force when the mass of 1 object doubles? What happens when the masses of both double? What happens when the distance doubles?

Newton’s 3 rd Law (Action-Reaction) When 1 object exerts a force on a 2 nd object, the 2 nd object exerts a force on the 1 st that is equal in magnitude but opposite in direction

Momentum Momentum-Inertia in motion Vector Depends on the mass AND velocity of an object – Momentum (p) = mass X velocity

Impulse (Ft) Impulse – Change in momentum Product of net force and the time interval over which it acts – F ∆ t = ∆ p OR F ∆ t = m ∆ v

Impulse (Ft) An equal change in momentum can be achieved by EITHER: 1. A large force for a short period of time 2. A small force for a long time

Work and Kinetic Ener gy Work-Product of the force exerted on an object and the distance the object moves in the direction of the force

Work – Work (W) = F d » OR – Work (W) = F d (cos Θ) Work is measured in Joules (J) 1 J = 1 N meter

Power Power- The rate of doing work Power = Work/time Measured in Watts Watt = 1 Joule of energy transferred in 1 second

Energy Energy- The ability to do work!

Kinetic Energy Kinetic Energy-The energy of an object due to motion KE = ½ m v ²

Work/Energy Theorem: The net work done on an object is equal to its change in kinetic energy F d = ½ m v ²

Gravitational Potential Stored energy of position GPE=mgh – Measured in Joules