Syllabus concepts to know

• A.2.1 Newton’s three laws of motion
• A.2.2 forces as interactions between bodies
• A.2.3 that forces acting on a body can be represented in a free-body diagram
• A.2.4 that free-body diagrams can be analysed to find the resultant force on a system
• A.2.5 the nature and use of the following contact forces ◦ normal force FN is the component of the contact force acting perpendicular to the surface that counteracts the body ◦ surface frictional force Ff acting in a direction parallel to the plane of contact between a body and a surface, on a stationary body as given by Ff ≤ μsFN or a body in motion as given by Ff = μdFN where μs and μd are the coefficients of static and dynamic friction respectively ◦ tension ◦ elastic restoring force FH following Hooke’s law as given by FH = –kx where k is the spring constant ◦ viscous drag force Fd acting on a small sphere opposing its motion through a fluid as given by Fd = 6πηrv where η is the fluid viscosity, r is the radius of the sphere and v is the velocity of the sphere through the fluid ◦ buoyancy Fb acting on a body due to the displacement of the fluid as given by Fb = ρVg where V is the volume of fluid displaced
• A.2.6 the nature and use of the following field forces ◦ gravitational force Fg is the weight of the body and calculated is given by Fg = mg ◦ electric force Fe ◦ magnetic force Fm
• A.2.7 that linear momentum as given by p = mv remains constant unless the system is acted upon by a resultant external force
• A.2.8 that a resultant external force applied to a system constitutes an impulse J as given by J = FΔt where F is the average resultant force and Δt is the time of contact
• A.2.9 that the applied external impulse equals the change in momentum of the system
• A.2.10 Δp that Newton’s second law in the form F = ma assumes mass is constant whereas F = allows for Δt situations where mass is changing
• A.2.11 the elastic and inelastic collisions of two bodies
• A.2.12 explosions
• A.2.13 energy considerations in elastic collisions, inelastic collisions, and explosions
• A.2.14 that bodies moving along a circular trajectory at a constant speed experience an acceleration that is directed radially towards the centre of the circle—known as a centripetal acceleration as given by v2 4π 2r a= = ω2r = 2 r T
• A.2.15 that circular motion is caused by a centripetal force acting perpendicular to the velocity
• A.2.16 that a centripetal force causes the body to change direction even if its magnitude of velocity may remain constant
• A.2.17 that the motion along a circular trajectory can be described in terms of the angular velocity ω which is 2πr related to the linear speed v by the equation as given by v = = ωr.