ASRJC Physics Forces Notes

ANDERSON SERANGOON JUNIOR COLLEGE PHYSICS 9749 4-1 Additional Notes Topic 4: Forces Learning Outcomes: Candidates should be able to: Types of forces (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. (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.) 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. 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. 1. How Submarines Work. Retrieved from (http://science.howstuffworks.com/transport/engines-equipment/submarine1.htm). 2. Cartesian diver. Retrieved from (http://physics.org/interact/physics-to-go/cartesian-diver/). 3. Biomechanics & High Jump. Retrieved from (https://www.topendsports.com/sport/athletics/biomechanics-highjump.htm)

ANDERSON SERANGOON JUNIOR COLLEGE PHYSICS 9749 4-2 Additional Notes • A force is a push or a pull, that is, a force is an interaction between two bodies or between a body and its environment. Hence we always refer to the force that one body exerts on another. • From the topic of Dynamics, Newton’s 2 nd Law states that the resultant force acting on a body is proportional to the rate of change of momentum of the body and the change in momentum takes place in the direction of the force. • Force is a vector quantity and requires both magnitude and direction for it to be fully defined. The SI unit for force is newton (N) and one newton is equal to 1 kg m s -2. • In th