FUNdamental Forces & FBD’s

What is a force? A push or a pull on an object. Let’s demonstrate Pick a partner (size appropriate) Stand 50cm apart from each other (feet shoulder width apart). Put your hands out to your sides with your palms facing your partner. Now the object is to keep your balance and knock your partner off balance by avoiding their attempts or by you hitting their hands ONLY.

Strong Nuclear Force It has the shortest range, meaning that particles must be extremely close before its effects are felt. Its main job is to hold together the subatomic particles of the nucleus . Strongest of the 4 fundamental forces.

Electromagnetic Force There are two kinds of electrical charge - positive and negative. The electrical force can be either attractive or repulsive - like charges repel, opposite charges attract. Although the Electromagnetic force is of order 1039 times stronger than Gravity, it is not as apparent because of its dual (attractive/repulsive) nature 2nd strongest of the 4 fundamental forces

Weak Nuclear Force It causes radioactive beta decay and other subatomic reactions. The particles that carry the weak force are called weakons (or intermediate vector bosons). 3rd Strongest of the 4 fundamental forces.

Gravitational Force It is a purely attractive, long-range force. We will learn Newton’s Law of Universal Gravitation tomorrow (stay tuned) Weakest of the 4 fundamental forces

Electroweak Force A force that unifies the electromagnetic and weak nuclear forces under conditions of extreme temperature prevalent much earlier in the history of the universe. Physicists concluded that the weak and electromagnetic forces have essentially equal strengths. This is because the strength of the interaction depends strongly on both the mass of the force carrier and the distance of the interaction.

How is a force measured? A Newton (N) is the unit of force 1 N = 1 kg * m s2 By looking at the units, the equation for force is F=ma (your new best friend) Forces are usually measured using a spring scale

Free Body Diagram’s (FBD’s) Here is the step by step how to draw one: Draw a north arrow and a scale Sketch of the object (don’t be too detailed) Locate the approximate centre of the object and put a dot there. Draw on the force arrows to represent each force on the object (just like vector diagrams). Do NOT include the forces that the object exerts on other objects.

Common Forces Normal Force (FN) – acts on an object perpendicular to the surface it is resting on Friction (Ff) – ALWAYS opposes motion Gravity (FG) – related to mass and is straight down Applied (FApp) – given by a external body

Example FBD’s

Adding Non-Collinear Forces It is the same as adding vector quantities that we did in chapter 1, but now we can use: Tail to Tip method again. Trig  - Sine Law Cosine Law  c2 = a2 + b2 - 2ab·cos(C) -

Homework p. 119 # 1,2 Have Fun 