Concept 3 Notes - Newton's Laws

Newton's Laws

Concept: It's not Rocket Science

Force

• Definition: A push or pull one object exerts on another.

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

  • Forces can change an object’s motion.

  • Multiple forces can act on an object simultaneously.

• Net Force: Combination of forces acting on an object.

  • Example: F = 2 N, F = 5 N

  • Net Force = 3 N to the left

Balanced and Unbalanced Forces

• Balanced Forces: Equal in size, opposite in direction, resulting in a net force of 0.

  • Example: F = 4 N, F = 4 N → Net Force = 0 N

• Unbalanced Forces: Not equal, causing motion in the direction of the larger force.

  • Example: F = 2 N, F = 3 N → Net Force = 6 N to the right

Newton’s 1st Law of Motion

• Definition: An object will continue at constant velocity unless a net force acts on it.

  • Objects in motion remain in motion; objects at rest remain at rest.

• Also known as the Law of Inertia.

  • Example: Slamming brakes causes body to lurch forward due to inertia.

  • Inertia: Resistance to change in motion; more mass = more inertia.

Forces Changing Motion

• Friction: Resistance when two objects contact.

• Air Resistance: Resistance an object experiences moving through air.

• Gravity: Attraction between two masses, pulling objects towards Earth.

Factors Affecting Friction

• Surface Roughness: Rougher surfaces increase friction due to more microwelds.

• Normal Force: Greater force pushing together increases friction.

• Surface Area: Increased contact area increases friction.

Types of Friction

• Static Friction: Between surfaces not moving past each other.

• Sliding Friction: Between surfaces sliding past each other.

• Rolling Friction: Between a rolling object and the surface.

Air Resistance (Drag)

• Determined by:

  • Speed: Greater speed increases resistance.

  • Size: Larger object increases resistance.

  • Shape: Flatter objects increase resistance.

Law of Universal Gravitation

• Masses exert an attractive force on each other.

  • Depends on:

    • Mass: Greater mass = greater attraction.

    • Distance: Closer distance = greater attraction.

Gravity

• Causes all falling objects to accelerate at 9.8 m/s², regardless of mass (ignoring air resistance).

Terminal Velocity

• Maximum velocity a falling object can reach when gravity and air resistance balance each other.

  • Net force = 0, thus no acceleration.

  • Example: Terminal velocity of humans is approximately 55 m/s.

Newton’s 2nd Law of Motion

• Definition: Net force causes an object to accelerate in the direction of the force.

  • Greater mass requires greater force to accelerate.

  • Greater net force results in greater acceleration.

• Formula: F = ma

Example Calculations

• If pushing a sled with a force of 40 N, and mass is 80 kg:

  • F = 40 N, m = 80 kg

  • Acceleration (a) = F/m = 0.5 m/s²

Weight

• Definition: Force of gravity on an object.

  • Calculated using F = ma, with a = 9.8 m/s² for gravity.

• Example Calculation:

  • Mass = 42 kg → Weight = (42)(9.8) = 411.6 N

Weight vs. Mass

• Mass: Amount of matter in an object, constant regardless of location.

• Weight: Changes based on gravitational pull; lower on moons, higher on larger planets.

Newton’s 3rd Law of Motion

• Definition: Every action has an equal and opposite reaction.

  • Example: Jumping on a trampoline; the trampoline exerts equal force in opposite direction.

Law of Conservation of Momentum

• Definition: Momentum (p) is the mass in motion; transferred in collisions.

  • Formula: p = mv (p = momentum, m = mass, v = velocity).

Example Calculations of Momentum

• Car with mass of 1300 kg at 28 m/s has momentum:

  • p = (1300 kg)(28 m/s) = 36,400 kg*m/s.

Conservation of Momentum in Collisions

• Momentum is conserved; transferred between colliding objects.

Example Collision Calculation

• Ball #1 (11 m/s) collides with Ball #2 (0.17 kg) at 9 m/s:

  • Calculate mass of Ball #1 using conservation of momentum.