Forces Types of Forces Effects of Forces Gravity

Forces Types of Forces Effects of Forces Gravity, Mass and Weight Newton’s Laws Freefall

What is force? Common symbol: F Unit: Newton, N Equivalent base units: kg-m-s-2

Mass versus Weight l Mass ¡ Amount of matter in an object ¡ unit: kilogram, kg ¡ Does not change with location l Weight ¡ Gravitational force on the object ¡ Unit: Newton, N ¡ Equal to l Mass x acceleration due to gravity lm x g l Where g = 9. 81 ms-2 ¡ Changes with location

Newton’s Third Law For every action there is an equal and opposite reaction Law of Action and Reaction

Weight Normal force Weight Air resistance

Weight Drag Friction Thrust Normal Force

Weight Drag Thrust Upthrust

Effects of Forces l Change shape ¡Rigid bodies l Change the state of motion ¡Move from rest ¡Speed up ¡Slow down ¡Stop ¡Change its direction l Newton’s Laws

Change of Shape

extension

Newton’s First Law If no unbalanced force acts on a body then the body is in equilibrium. Law of Inertia

When the forces are balanced l The body does not move l The body moves ¡At a constant speed ¡In the same direction

Balanced forces

Balanced Forces The book stays still!

Balanced Forces The airplane moves forwards at constant speed!

Balanced Forces Drag Thrust Friction The car moves at constant speed!

Newton’s Second Law l An unbalanced force changes the motion of an object. ¡ It speeds up ¡ Or slows down ¡ Or changes direction ¡ Or changes speed and direction l Acceleration ¡ change in motion l Equation ¡a = force mass

Unbalanced Forces The car moves from rest. The car speeds up.

Unbalanced Forces The car slows down to stop. The car slows down.

The Physics of Falling l Freefall ¡Motion where only gravity is acting on the body ¡Acceleration due to gravity, g ¡Air resistance is negligible

The Physics of Skydiving

The Physics of Falling with Air Resistance l Terminal Velocity ¡The maximum speed of a falling object ¡When upward forces balance downward forces on the object

The End