Physics

​What is speed?

​Speed is a measure of the rate at which an object moves over a distance.

Average speed can be calculated by dividing the distance travelled by the time taken.

Calculate average speed of an object using speed = distance/time.

(a) The average speed of an aeroplane that travels from Perth to Melbourne, a distance of 2730 km by air, in 3 hours is: v = d t = 2730 km 3h = 910 km/h.
The formula can also be used to express the speed in m/s. v = d t = 2730000 m 3 × 3600 s (converting kilometres to metres and hours to seconds) = = 25m/s.
(b) The average speed of a snail that takes 10 minutes to cross an 80 cm concrete paving stone in a straight line is: v = d t = 80 cm 10 min = 8 cm/min.

Newton’s First Law of Motion states that an object will remain at rest, or will not change its speed or direction, unless it is acted upon by an outside, unbalanced force.
In many maneuvres that you may experience as a passenger on a bus, an unbalanced force is acting on the vehicle to change its speed or direction

Calculate the weight of an object

CALCULATING WEIGHT AT THE EARTH’S SURFACE
The force of gravitational attraction towards a large object like a planet is called weight.
The weight (in newtons) of any object can be calculated using the formula: weight = mg where m = mass (in kilograms)              g = gravitational field strength (in N/kg).
At the Earth’s surface, the gravitational field strength is 9.8 N/kg. That is, the gravitational force acting on each kilogram of mass is 9.8 N. The weight of a 1 kg object is therefore: weight = mg = 1kg × 9.8 N/kg = 9.8 N. The weight of a 2000 kg bus is: weight = mg = 2000 kg × 9.8 N/kg = 19600 N.

Newton’ Second Law of Motion using the formula
Force = mass x acceleration

Newton’ Second Law of Motion using the formula
Force = mass x acceleration

Newton’s Second Law of Motion describes how the mass of an object affects the way that it moves when acted upon by one or more forces.

For example, when two men pull in opposite directions on the box shown in the diagram at right, the net force is 40N to the right. The vertical forces can be ignored because the weight of the box and the upward push of the floor are equal and opposite in direction. If the floor is smooth, friction can be ignored.

In symbols, Newton’s second law can be expressed as: a = F m where a = acceleration F = the net force on the object m = the mass of the object.

The net force is the total force acting on the object. If the net force is measured in newtons (N) and the mass is measured in kilograms (kg), the acceleration can be determined in metres per second squared (m/s2 ).