Do now!

Forces Remember a force is a push (or pull)

Forces Force is measured in Newtons

Forces There are many types of forces; electrostatic, magnetic, upthrust, friction, gravitational………

Scalars and Vectors scalars vectors Magnitude (size) No direction Magnitude and direction temperaturemass speed velocity force acceleration

Representing vectors Vectors can be represented by arrows. The length of the arrow indicates the magnitude, and the direction the direction!

Adding vectors For example; 6 N4 N 2 N Resultant force Copy please!

Robert Hooke

Investigating forces and springs You are going to investigate how much a spring stretches when a force is applied to it. The amount a spring stretches is called its extension. This is the difference in length between the stretched spring and the length of the spring when it was unstretched. (Remember we are looking at the force on the spring. A mass of 100g will have a weight (force of gravity pulling it down) of 1 Newton. Add masses to your spring and carefully measure its extension. You can do this until the spring breaks! (but you must wear goggles and be careful during this investigation). Your experimental report will include the following A table of results A graph of your results A conclusion describing what you have discovered (think about this!)

Table of results Force (N)Length of spring (cm) Extension (cm)

Graph Force (N) Extension (cm)

Go!

Hooke’s law (F = kx) Force (N) Extension (x) (cm) L imit of proportionality The extension of a spring is proportional to the force applied (until the limit of proportionality is reached). The gradient of the graph is equal to k, the spring constant.

Steel, glass and wood! Force Extention Even though they don’t stretch much, they obey Hooke’s law for the first part of the graph

Rubber Force Extension