Some definitions: Weight vs mass Mass is amount of matter in an object. Measured with a balance in kilograms Weight is the force of gravity on that mass. Measured with a scale in Newtons. Any force is measured in newtons (N). Use of spring scale & Balance.

Some definitions: Force & acceleration Force is a push or a pull. Force is measured in Newtons. If forces are balanced, object doesn’t move or remains in constant motion at the same speed. If forces become unbalanced, a change in state of motion occurs. Acceleration is a change in velocity over time. a = change in velocity or Δ v / t. Since v is distance/time or m/s then the units for acceleration are some distance / unit of time squared. Ie: m/s2, miles/hr/hour etc.

Newton’s First Law, Lesson 3 Laziness

Inertia Inertia is determined by mass. The more mass an object has, the harder it is to change its state of motion. More mass = more inertia =more force needed to stop or move an object. Examples: coins, egg drop, tablecloth.

Friction Invisible force. Caused by surface irregularities rubbing each other. Air resistance (or drag) is a type of friction. Safety bumpers are now concrete – more friction. Video.

Newton’s second law, Lesson 3 States the relationship between force, acceleration and mass. Law: The amount of force on an object needed to produce a given change in the state of motion of an objects upon its mass. The more mass, the more force required to change its velocity (or motion). Therefore a large mass needs a large force acting on it to change the motion.

Net force is the actual force acting on an object, causing it to move or to stop

Example Using F = m a….. How much force is required to accelerate a car at an average acceleration of 60 m/s2 if the car has a mass of 2000 kg? We want to find F. m = 2000 kg. The acceleration (a) we want to be 60 m/s2 So F = m a which is 2000 kg (60 m/s2) or 120,000 N Now you try one. We know a wagon is accelerating at 2 m/s2 and its mass is 400 kg. What is the force acting on the wagon?

Newton’s third law, Lesson 3

Equal and opposite reactions

Gravity, Lesson Four Law of Universal Gravitation also was developed by Issac Newton. Gravity is the force of attraction between the masses of any two objects. Two factors that affect the strength of gravity are: the mass of each object, and the distance between the objects.

Gravitational force

Revisiting mass & weight Weight = m a F = m a F = m g, so w = m g or Weight = mass x force of gravity

Acceleration due to gravity Falling objects (on Earth) increase velocity about 10 m/s every second. (actually 9.8 m/s) Terminal velocity is where the force of gravity = the force of air resistance or air ‘drag.’ Falling objects continue speeding up (or accelerating) until they reach terminal velocity.

Terminal velocity All objects on earth fall at the same acceleration HOWEVER…. Objects with greater surface area have more air resistance (friction) & take longer to reach terminal velocity. (ie. feather and a bowling ball). Heavier objects seem to fall faster because they have a higher terminal velocity than lighter objects.