Forces 1

• The SI unit of force is the Newton (N).
• A vector quantity has both magnitude and direction.
• For every action, there is an equal and opposite reaction.
• Weight = mass × gravitational field strength (W = mg).
• Friction is the force that opposes motion between two surfaces.
• Magnetic force is the force that acts at a distance and can attract or repel objects.
• Centripetal force is the type of force that causes an object to move in a circle.
• Air resistance (or drag) is the force that acts on an object moving through air.
• The unit of pressure is Pascal (Pa).
• The resultant force is the overall force acting on an object when all individual forces are combined.
• The object remains stationary because the resultant force is zero.
• There is no change in motion or acceleration.
• Weight = mass × gravitational field strength.
• Weight = 5 × 9.8 = 49 N.
• Moment is the turning effect of a force around a pivot.
• The unit of moment is Newton meter (Nm).
• The acceleration doubles if the resultant force on an object is doubled.
• This is because acceleration is directly proportional to force (F = ma).
• The longer the lever arm, the greater the moment for the same force.
• Moment = force × distance from the pivot.
• The forward force (thrust) is balanced by the opposing forces (air resistance and friction).
• The resultant force is zero, hence the car moves at constant speed.
• As the object accelerates, air resistance increases until it equals the weight of the object.
• At this point, the resultant force is zero, so the object falls at a constant speed (terminal velocity).
• The gravitational field strength on the Moon is weaker than on Earth.
• Therefore, the weight, which depends on gravitational field strength, is less on the Moon.
• The force of friction (including air resistance) is greater than the thrust provided by the cyclist.
• This results in a resultant force that opposes the motion, causing deceleration.
• The reading would be lower if a mass were hung from a spring balance on the Moon rather than on Earth.
• This is because the gravitational field strength on the Moon is less than on Earth.
• Use Pythagoras' theorem to find the magnitude: Resultant force = √(F₁² + F₂²).
• Determine the direction using trigonometry: tan(θ) = F₂/F₁.
• The resultant force is the vector sum of the two forces.
• For an object to be in equilibrium, the sum of the clockwise moments must equal the sum of the anticlockwise moments.
• Calculate the moments about a pivot: Moment = Force × Distance from pivot.
• If the total clockwise moment equals the total anticlockwise moment, the object is in equilibrium.
• Pressure is inversely proportional to the surface area: P = F/A.
• Increasing the surface area decreases the pressure for the same force.
• Therefore, the object exerts less pressure on the ground when the surface area is increased.
• Horizontal component: Fₓ = 60 cos(30°) = 60 × 0.866 = 51.96 N ≈ 52 N.