# Forces, density and pressure – CIE AS Level Physics 9702

Contents:-

• Types of force
1. describe the force on a mass in a uniform gravitational field and on a charge in a uniform electric field
2. understand the origin of the upthrust acting on a body in a fluid
3. show a qualitative understanding of frictional forces and viscous forces including air resistance (no treatment of the coefficients of friction and viscosity is required)
4. understand 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
1. define and apply the moment of a force
2. understand that a couple is a pair of forces that tends to produce rotation only
3. define and apply the torque of a couple
• Equilibrium of forces
1. state and apply the principle of moments
2. understand that, when there is no resultant force and no resultant torque, a system is in equilibrium
3. use a vector triangle to represent coplanar forces in equilibrium
• Density and pressure
1. define and use density
2. define and use pressure
3. derive, from the definitions of pressure and density, the equation Δp = ρgΔh
4. use the equation Δp = ρgΔh

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