Physics Class: Measuring Motion

Measuring Motion

• Two key aspects of measuring motion: Change in position and Change in time
• Three significant combinations of length and time: Speed, Velocity, and Acceleration

Speed

• Speed is the change in position related to time.
• Average Speed is the most common measurement. Calculated by dividing the total distance by the elapsed time.
• Instantaneous Speed is the speed at a specific moment in time, where the time interval approaches zero.

Velocity

• Velocity describes both the speed of an object and its direction.
• Velocity is represented graphically as vectors, where the length represents the magnitude (speed) and the arrowhead indicates the direction.

Acceleration

• Acceleration describes the change in motion over time and can involve changes in speed, direction, or both.
• Acceleration is calculated by dividing the change in velocity by the elapsed time.

Forces

• Force is a push or pull that can change an object’s motion.
• The net force on an object is the sum of all forces acting on it, determining its overall effect.

Four Fundamental Forces

• Gravitational Force acts between all objects with mass
• Electromagnetic Force acts between electrically charged parts of atoms.
• Weak Nuclear Force is involved in certain nuclear reactions.
• Strong Nuclear Force is responsible for holding the nucleus together. It is the strongest force in the universe.

Horizontal Motion on Land

• Inertia is the tendency of an object to resist changes in its motion, including rest.
• An object in motion will continue moving at a constant velocity unless acted upon by an unbalanced force.

Balanced and Unbalanced Forces

• Balanced forces result in no change in motion.
• Unbalanced forces can cause changes in speed or direction.
• A retarding force decreases speed. A boosting force increases speed. A sideways force changes direction.

Falling Objects

• Free fall occurs when an object falls only under the influence of gravity without air resistance.
• The distance fallen is proportional to the square of the time elapsed.
• The velocity increases at a constant rate.
• The acceleration due to gravity (g) is the same for all objects.

Compound Motion

• Projectile motion combines vertical motion and horizontal motion.
• Gravity acts constantly on a projectile.
• The acceleration due to gravity (g) is independent of the object's motion.

Projectile Motion

• Vertical projectile motion:
  • The object slows down going up.
  • Comes to a stop at the highest point.
  • Accelerates downwards.
• Horizontal projectile motion:
  • Horizontal velocity remains constant (neglecting air resistance).
  • Combined with vertical motion, results in a curved path.

Fired Horizontally vs. Dropped

• An object fired horizontally and an object dropped from the same height will reach the ground at the same time.
• The vertical motions occur in parallel, but the fired object has an additional horizontal motion component.

Example: Passing a Football

• The only force acting on a football is gravity.
• The vertical velocity decreases, stops, and then increases.
• The horizontal motion is uniform.
• The combination of vertical and horizontal motion results in a parabolic path.

Newton’s Laws of Motion

• Sir Isaac Newton (1564-1642 AD), developed the three laws of motion.
• Newton's laws are based on the concept of forces.

Newton’s First Law of Motion (The Law of Inertia)

• An object at rest will stay at rest, and an object in motion will stay in motion at a constant velocity unless acted upon by an unbalanced force.
• Inertia is the resistance of an object to changes in its motion.

Newton’s Second Law of Motion

• Forces cause acceleration.
• Force (F) is directly proportional to mass (m) and acceleration (a): F = ma
• The unit of force is the Newton (N).
• More force produces more acceleration.
• More mass produces less acceleration.

Example: Newton’s Second Law

• A smaller object accelerates faster than a larger object when acted upon by the same force.

Weight and Mass

• Mass is the amount of matter in an object and is a measure of its inertia.
• Weight is the force of gravity acting on an object's mass.
• Pounds and Newtons measure force.
• Kilograms measure mass.

Newton’s Third Law of Motion

• For every action, there is an equal and opposite reaction.
• When two objects interact, the force on one object equals the force on the other object in magnitude but opposes it in direction.

Momentum

• A property related to Newton's Second Law of Motion.
• Momentum (p) is the product of an object's mass (m) and its velocity (v): p = mv.
• Momentum considers both motion (velocity) and inertia (mass).

Conservation of Momentum

• In the absence of external forces, the total momentum of a system remains constant.
• In a closed system, the momentum transferred in one direction equals the momentum transferred in the other direction.

Impulse

• Impulse is defined as the force acting on an object over a specific time interval.
• Impulse produces a change in momentum.
• Applications:
  • Airbags
  • Padding for elbows and knees
  • Protective plastic barrels on highways

Forces and Circular Motion

• Circular motion is a type of accelerated motion where the direction of velocity is continuously changing.
• Centripetal acceleration is necessary for circular motion.
• Centripetal force (directed towards the center) is required to maintain circular motion.
• Centrifugal force is the apparent outward force felt as an object's direction changes.
• If the centripetal force ends, the object will move in a straight line.

Newton’s Law of Gravitation

• A fundamental force of attraction that exists between all objects with mass.
• The force is proportional to the product of the masses.
• The force is inversely proportional to the square of the separation distance.
• Gravitational constant (G): 6.67 x 10^-11 N*m^2/kg^2
• Acceleration due to gravity (g) is caused by Newton's Law of Gravitation.
• Satellites orbit Earth due to the combination of their tangential velocity and Earth's gravitational force.
• Geosynchronous satellites have an orbital period of one day, causing them to appear stationary from Earth.

Explore the foundational concepts of measuring motion in physics, including speed, velocity, and acceleration. Learn how to calculate average and instantaneous speed, and understand the significance of direction in velocity. This quiz will enhance your understanding of motion dynamics.