forces

• Newton's three laws of motion are universal laws that can be used to model the motion of objects
• Newton's first law states that an object will remain at rest or continue to travel with constant velocity unless acted upon by a resultant force
• Newton's third law explains that when two objects interact, they exert equal and opposite forces on each other
• All forces, including gravitational, electromagnetic, strong nuclear, and weak nuclear forces, obey Newton's third law
• Newton's second law states that the net force acting on an object is directly proportional to the rate of change of momentum, and is acting in the same direction
• Linear momentum, p, of an object is defined as the product of the object’s mass, m, and its velocity v: p = mv. The SI unit for momentum is kgms-1
• F = ma is a special case of Newton’s second law, true when the mass of the object remains constant during its motion
• Impulse of a force is defined as the product of the force and the time for which it acts: impulse = force × time
• In collisions, conservation of momentum states that the total initial momentum will be equal to the total final momentum if no external forces act on the system
• In perfectly elastic collisions, the total kinetic energy of the system remains constant, while in inelastic collisions, some kinetic energy is lost to other forms like heat and sound energy
• For one-dimensional collisions, the conservation of momentum can be formulated as: m1u1 + m2u2 = m1v1 + m2v2
• In two-dimensional collisions, conservation of momentum applies separately in the x and y directions
• Factors affecting how far projectiles like cannonballs can travel include the height of the cannon above the sea and the initial velocity of the ball
• In projectile motion, the horizontal velocity remains constant because the horizontal acceleration is zero
• In projectile motion, the vertical velocity changes due to the acceleration of free fall, allowing for the calculation of vertical displacement and time of flight
• The acceleration of free fall is denoted by the label g and has the unit m s^-2
• The value for g varies depending on factors like altitude, latitude, and geology of an area, with a general value of 9.81 m s^-2 used
• Stopping distances have two components: thinking distance and braking distance
• Thinking distance is the distance traveled between seeing a reason to stop and using the brake, calculated as speed x reaction time
• Equations of motion for constant acceleration in a straight line are known as the suvat equations
• Area under the graph: acceleration can be determined from the gradient of a velocity time graph
• Acceleration is defined as the rate of change of velocity, a = Δv / Δt, where Δv is the change in velocity and Δt is the time taken for the change
• Acceleration is a vector quantity with magnitude and direction; a negative acceleration is often called deceleration
• For non-linear velocity-time graphs, the area under the graph can be determined by counting squares: count complete or nearly complete squares, then count the remaining squares mostly beneath the graph, omitting squares mostly above the graph
• Displacement can be calculated from the area under the velocity time graph: the change in displacement is equal to the area under the graph, which represents the total displacement of the object
• Displacement is easy to calculate when acceleration is constant, as areas can be broken down into rectangles and right-angled triangles
• Scalar and vector quantities: displacement is a vector quantity with magnitude and direction, while distance is scalar; velocity is a vector quantity calculated from displacement