Forces Quiz attempt 2

Newton’s Laws of Motion

• Newton’s First Law (Inertia): An object at rest stays at rest, and an object in motion stays in motion unless acted on by a net force.

• Newton’s Second Law: Fnet=maF_{\text{net}} = maFnet​=ma (Net force = mass × acceleration)

• Newton’s Third Law: For every action, there is an equal and opposite reaction.

Weight and Gravity

• Weight (Force of Gravity): Fg=mgF_g = mgFg​=mg

  • mmm = mass (kg)

  • g=9.8 m/s2g = 9.8 \, \text{m/s}^2g=9.8m/s2

Friction

• Friction Formula: f=μNf = \mu Nf=μN

  • μ\muμ = coefficient of friction

  • NNN = normal force

• Friction Direction: Always opposes motion.

Normal Force

• On a Flat Surface: N=mgN = mgN=mg (if no vertical forces other than weight)

• On an Incline: N=mgcos⁡θN = mg \cos \thetaN=mgcosθ

• With an Upward Pull: Normal force decreases.

• With a Downward Push: Normal force increases.

Forces on an Incline

• Parallel Force (down the ramp): F∥=mgsin⁡θF_{\parallel} = mg \sin \thetaF∥​=mgsinθ

• Perpendicular Force (normal force): F⊥=mgcos⁡θF_{\perp} = mg \cos \thetaF⊥​=mgcosθ

Tension

• At Rest or Constant Speed (vertical): T=mgT = mgT=mg

• Accelerating Upward: T=mg+maT = mg + maT=mg+ma

• Accelerating Downward: T=mg−maT = mg - maT=mg−ma

Force Components at an Angle

• Horizontal Component: Fx=Fcos⁡θF_x = F \cos \thetaFx​=Fcosθ

• Vertical Component: Fy=Fsin⁡θF_y = F \sin \thetaFy​=Fsinθ

Kinematic Equations (if needed)

• v=v0+atv = v_0 + atv=v0​+at (final velocity)

• d=v0t+12at2d = v_0 t + \frac{1}{2}at^2d=v0​t+21​at2 (displacement)

• v2=v02+2adv^2 = v_0^2 + 2adv2=v02​+2ad (velocity with displacement)

Quick Rules to Remember

• Constant velocity → net force = 0 (forces are balanced)

• Acceleration → net force ≠ 0 (use Fnet=maF_{\text{net}} = maFnet​=ma)

• Friction always opposes motion.

• Pulling upward reduces the normal force.

• Pushing downward increases the normal force.

• On an incline, gravity pulls parallel and perpendicular to the surface, not straight down.