11SCI - Mechanics

Finn LeSueur

2020

Copy these learning outcomes and the date into your books!

- Recap forces
- Explain force and pressure in terms of everyday situations. Use \(P = F/A\).

Calculate the **net** force acting upon these objects:

What does an unbalanced force do to the motion of an object?

It causes the object to accelerate (or de-accelerate).

We know this because of the equation

\[\begin{aligned} force &= mass\times acceleration \\ F &= m \times a \end{aligned}\]For the followig equation give the **name** and **unit** for each variable in the equation.

- F stands for
**force**and has units**Newtons (N)** - m stands for
**mass**and has units**kilograms (kg)** - a stands for
**acceleration**and has units**meters per second squared (\(ms^{-2}\))**

- What do you think of when you think of pressure?
- What affects the pressure exerted by an object?

The most classic case of pressure is sharpening a knife. Why do we sharpen knives? What does sharpening a knife change about the knife?

Pressure is defined as: *the amount of force per square meter*.

- Force is measured in
**Newtons (N)** - Area is measured in
**meters squared (\(m^{2}\))**

- Therefore, pressure is measured in Newtons per meters squared (\(\frac{N}{m^{2}}\) OR \(Nm^{-2}\))
- This is also known as a Pascal (Pa): \(Pa = \frac{N}{m^{2}} = Nm^{-2}\)

- Calculate the
**pressure**created by a force of \(3N\) with an area of \(0.5m^{2}\) - Calculate the
**pressure**created by a force of \(3N\) with an area of \(0.25m^{2}\) - Calculate the
**pressure**created by a force of \(3N\) with an area of \(0.125m^{2}\)

- Calculate the
**area**that a force (\(5N\)) is acting through if it has a pressure of \(7Pa\) - Calculate the
**area**that a force (\(7N\)) is acting through if it has a pressure of \(3Pa\) - Calculate the
**area**that a force (\(10N\)) is acting through if it has a pressure of \(3Nm^{-2}\)

- Calculate the
**force**of an object with area \(0.25m^{2}\) and pressure \(5Pa\) - Calculate the
**force**of an object with area \(0.5m^{2}\) and pressure \(7Pa\) - Calculate the
**force**of an object with area \(0.75m^{2}\) and pressure \(10Pa\)

We are going to:

- Calculate our weights
- Find the area of our feet
- Calculate the pressure we all exert on the ground!

Jacob bikes down The Flying Nun. He and his bike have a mass of \(82kg\) and he accelerates at \(0.8ms^{-2}\).

- Calculate the
**net force**acting upon Jacob and his bike to cause this acceleration - Draw a force diagram showing the forces acting upon Jacob as he accelerates
- Describe the size and direction of the forces compared to each other (horizontal and vertical)

Giovanni is running a 100m sprint. Each of his feet have a surface area of \(200cm^{2}\) (\(0.0200m^{2}\)), which sink into the track. Together, his feet exert a pressure of \(13000Pa\). Calculate Giovanni’s weight.

Because **weight** is a force, we know that we are looking for \(F\).

**Homework:**Education Perfect due Monday 29th 11:25am- sciPAD Page 46