Higher Physics - Dynamic Universe (Forces, Energy and Power + Collisions, Explosions and Impulse)

Force Equation

F = ma where:

F = Force

m = Mass

a = Acceleration

Weight

Downward force on an object due to gravity, can be calculated with W=mg where:

W = weight

m = Mass

g = Gravity

Note: Gravity always 9.8ms^-2 unless stated otherwise in question

Weight Component Down Slope

To find component down a slope (parallel to direction of slope) use w=mg sinθ where:

• w = Weight

• m = Mass

• g = Gravity

• θ = Angle of slope

Weight Component 90° to Slope

To find component 90° to a slope (perpendicular to direction of slope) use w=mg cosθ where:

• w = Weight

• m = Mass

• g = Gravity

• θ = Angle of slope

Different Types of Force

• Friction - Opposes motion, created by surfaces rubbing together

• Air resistance/drag - Force opposing motion as an object moves through air

• Tension - Pulling force of an object like rope, cable etc.

• Reaction - Force from contact of surface, always perpendicular (90°) to surface

Terminal Velocity

When forces on an object are balanced while in motion (force of motion and force opposing motion are equal)

Conservation of Energy

• Energy cannot be created or destroyed

• Can only be converted between forms

Kinetic Energy Formula

Kinetic energy can be calculated through E_k = ½ mv² where:

• E_k = Kinetic Energy

• m = Mass

• v = Velocity

Potential Energy

Potential Energy can be calculated with E_p = mgh where:

• E_p = Potential Energy

• m = Mass

• g = Gravity

• h = Height

Work Energy

Work Energy can be calculated by E_w = fd where:

• E_w = Work Energy

• f = Force

• d = Distance

Power

Rate at which energy is transferred, measured in watts (W) and can be calculated through the equation P = E/t where:

• P = Power

• E = Energy

• t = Time

Momentum

Vector quantity measured in kgms^-1, product of mass and velocity and calculated through the equation p=mv where:

• p = Momentum

• m = Mass

• v = Velocity

Conservation of Momentum

During collision/explosion, total momentum before = total momentum after

Elastic Collisions

Both momentum and kinetic energy are conserved

Inelastic Collisions

Momentum is conserved, but kinetic energy is not (lost as heat)

Impulse

Impulse is the force exerted on an object over a period of time (Ft), and is equal to the change of momentum to an object, therefore can be calculated through the equation Ft = mv - mu where:

• F = Force

• t = Time

• m = Mass

• v = Final Velocity

• u = Initial Velocity

Impulse Rules

• Longer contact time/smaller force = less impulse

• During collision between two objects impulses are equal in size but opposite in direction