HCI 04 Forces Lecture Notes

Hwa Chong Institution (College) H2 Physics C1 2023 Chapter 4 Forces “The same principle that allows an airplane to rise off the ground by creating lift under its wings is used in reverse in F1 cars to generate an additional ‘downward force’ to press the race car against the surface of the track. This increases the contact force between the tires and the road surface, allowing the car to turn corners at amazing speeds. F1 cars achieve down ward force-to-weight ratio of 1:1 at about 125 km/h. At 190 km/h (118 mph) the ratio is roughly 2:1.” - Anonymous Formula One Expert

Hwa Chong Institution (College) H2 Physics C1 2023 2 TOPIC 4: Forces H2 Physics Syllabus 9749 Forces Learning Outcomes Students should be able to: Types of force (a) recall and apply Hooke’s law (F = kx, where k is the force constant) to new situations or to solve related problems (b) describe the forces on a mass, charge and current-carrying conductor in gravitational, electric and magnetic fields, as appropriate (covered later in relevant chapters) (c) show a qualitative understanding of normal contact forces, frictional forces and viscous forces including air resistance (no treatment of the coefficients of friction and viscosity is required) (partly covered in Kinematics) Centre of gravity (d) show an understanding that the weight of a body may be taken as acting at a single point known as its centre of gravity (covered in Dynamics) Turning effects of forces (e) define and apply the moment of a force and the torque of a couple (f) show an understanding that a couple is a pair of forces which tends to produce rotation only (g) apply the principle of moments to new situations or to solve related problems Equilibrium of forces (h) show an understanding that, when there is no resultant force and no resultant torque, a system is in equilibrium (i) use a vector triangle to represent forces in equilibrium Upthrust (j) derive, from the definitions of pressure and density, the equation p = ρgh (k) solve problems using the equation p = ρgh (l) show an understanding of the origin of the force of upthrust acting on a body in a fluid (m) state that upthrust is equal in magnitude and opposite in direction to the weight of the fluid displaced by a submerged or floating object (n) calculate the upthrust in terms of the weight of the displaced fluid (o) recall and apply the principle that, for an object floating in equilibrium, the upthrust is equal in magnitude and opposite in direction to the weight of the object to new situations or to solve related problems.

Hwa Chong Institution (College) H2 Physics C1 2023 3 Contents Topic 4: Forces 4.1 Hooke’s Law .............................................................................................................. 4 4.2 Upthrust or Buoyant Force ............................................................