PHYSICS EXAM

Kinematics

The study of motion

Depends on our point of reference

Are we curently in motion?

Motion

Movement of an object from one place to another, as measured by an observer.

If the line segment between the object and the observer changes in length, direction or both.

How can you tell if an object is in motion relative to another?

Uniform motion

Motion at a constant speed in a constant direction

Non-uniform motion

Movement that involves a change in speed, direction or both.

Scalar

Quantity that has only magnitude (size)

Vector

Quantity that has both magnitude (size) and direction

Distance

total length of the path travelled by an object in motion

Position

Distance and direction of an obejct from a particular reference point

Displacement

The change in position of an object

Resultant displacement

A common term for total displacement is…

Vector scale diagram

Representation of motion using vectors drawn to scale

Speed

distance travelled per unit of time (scalar)

Velocity

displacement of an object per unit of time (vector)

Instantaneous velocity

Velocity at a specific moment in time

Acceleration

Change in velocity per unit of time (vector)

Galileo Galilei

Who discovered acceleration due to gravity?

Projectile

An object that moves along a two dimensional parabolic trajectory due to gravity

Force

• A push or pull

• Causes objects to change their motion and/or shape

• Vector

• Measured in newtons (1 N = 1kg*m/s²)

• Gravitational force

• Electromagnetic force

• Strong nuclear force

• Weak nuclear force

What are the types of forces?

Gravitational Force

• Known as “force of gravity” or “weight”

• Attraction ONLY

• Acts between all objects in the universe

• Weak force but long range

Electromagnetic Force

• Caused by electric charges

• Most common (i.e. light, electricity, magnetic attraction)

• Strong force and long range

Strong nuclear force

• Holds protons and neutrons together in the nucleus of an atom

• Strongest force but very short range

Weak nuclear force

• Responsible for radioactive decay

• Strong force but very short range

Force of Gravity (F_g)

Force of attraction between Earth and object

Normal Force (F_n)

Force perpendicular to surface upon which object rests

Friction Force (F_f)

Force that opposes (attempted) motion of object

Applied Force (F_a)

Force exerted on object

Tension Force (F_t)

Force exerted by string or rope on object

Free-body diagram

Simple drawing representing the object being analyzed and all the external forces acting on it

Net Force (F_net)

• Vector sum of all the forces acting on an object

• Also known as the resultant force

  (Fnet= F1 + F2 + …)

Inertia

• Property of matter that causes it to resist changes in motion

• Is directly proportional to the mass of the object

Newton’s first law of motion

• Also known as the law of inertia

• If the net external force on an object is zero, the object will remain at rest or continue to move at a constant velocity

Implications of Newton’s first law of motion

1. Objects at rest tend to remain at rest

2. Objects in motion tend to remain in motion

3. If the velocity is constant, the net force acting on it must be zero

4. If the velocity is changing (in direction and/or magnitude) the change must be caused by a net external force acting on the object

Newton’s second law of motion

Fnet=ma

Newton’s third law of motion

• Every action has an equal opposite reaction

• The action and reaction forces act on different obejcts

• F_action = -F_reaction

Gravitational Field Strength (g)

• Force per unit mass acting on an object in a gravitational field (N/kg)

• Decreases as altitude increases

• Varies according to location since Earth is not a perfect sphere

• On Eeaarth g=9.8N/kg or 9.8m/s²

Mass

• Quantity of matter in an object (kg)

• Constant - only changes if the quantity of matter changes

• Measured using a balance

Weight (F_g)

• Measure of the force of gravity acting on object (N)

• Varies - depends on the magnitude of g at that location

• Measured using a spring scale or a force sensor

Weightlessness or Micro Gravity

• Terms often used to describe falling objects

• Are misleading because gravity is still in effect

• A better explanation is the object is experiencing a constant free-fall effect

Static Friction (F_s)

Force that prevents a stationary object from starting to move

Kinetic Friction (F_k)

• Force that acts against an object in motion

• Includes sliding friction, rolling friction, fluid friction

Friction

• can wear out machines, reduce efficiency, cause unwanted heat, etc.

• Can be controlled by: Making surfaces smooth, using materials with little friction, lubricating with grease or oil and using ball bearings

• rolling friction is a type of static friction

Mechanical Work

Occurs when a force displaces an object in the direction of the force or a component of the force

Work

is a scalar quantity (W=FchangeindD)

Positive work

• The force and displacement are in the same direction

• The speed of the object tends to increase

Negative work

• The force and displacement are in opposite directions

• The speed of the object tends to decrease

Zero work

When no work is done on the object

Energy (E)

• The capacity to do work

• Comes in many forms

• Scalar

• Joules

Kinetic energy

The energy possessed by a moving object

Potential energy

A stored form of energy

Gravitational Potential Energy

The energy possessed by an object due to it’s position relative to Earth

Mechanical energy

The sum of an object’s kinetic energy and gravitational potential energy

Work-energy principle

The net amount of mechanical work done on an object is equal to the object’s change in energy

Forms of energy

• Thermal

• Nuclear

• Elastic

• Electrical

• Gravitational

• Sound

• Radiant

• Kinetic

• Chemical

Heat

• Transfer of thermal energy from a warmer substance to a cooler one

• Occurs until both substances are at the same temperature

Energy transformation

Change of energy from one form to another

Law of conservation of energy

• Energy is neither created nor destroyed

• When energy changes from one form to another no energy is lost