Unit 2 - Forces
In this unit, you will be able to:
1. Define and describe concepts related to force – i.e. types of forces
2. State and apply Newton’s three laws of motion
3. Analyze the mathematical relationship among net force, mass and acceleration
4. Define and describe concepts related to the force of friction and gravity
5. Analyze the gravitation force acting on an object on the Earth’s surface
6. Design and carry out experiments to identify how friction affects the motion of
a sliding object
Pg. 53 Reflect on Your Learning
Forces in Nature
• force is described as a push or pull on an object
• forces are everywhere and act on almost anything
• a force applied to an object will sometimes change the shape and/or motion
of the object
• force is a vector quantity - it has magnitude and direction
• the symbol for force is 𝐹 and it’s unit is the Newton (N)
• one Newton is the amount of force required to accelerate a one
kilogram object at one metre per second. (1N = 1 kg•m/s2)
The Four Fundamental Forces
1. Gravitational force (weakest)
• force of attraction between all objects in the universe
2. Electromagnetic force
• force caused by electric charge
3. Strong nuclear force
• holds protons and neutrons together in the nucleus
4. Weak nuclear force
• responsible for the fact that some nuclei are radioactive
Common Forces
𝐹𝑔 - force of gravity
𝐹𝑁 - normal force – force perpendicular to the surface of objects in contact
𝐹𝑓 - force of friction – force between objects in contact and parallel to contact surface
𝐹𝑇 - tension – force exerted by string or ropes
𝐹𝐴 - applied force – pushing
Free Body Diagrams
A vector diagram showing all the forces acting simultaneously on an object is
called a free body diagram.
Drawing F.B.D.’s:
1.
2.
3.
4.
Draw compass point and suitable scale
Sketch the object isolated from it’s surroundings
Locate the centre of the object
Draw all force vectors acting on the object (note: always from the centre)
i.e. FBD for a car travelling at constant speed
𝐹𝑁
1 cm = 1 N
𝐹𝑓
𝐹𝐴
𝐹𝑔
Draw F.B.D.’s for the following situations:
1. A car accelerating
2. A car slowing down
3. A car travelling at constant speed up a hill
FBD Simulator
2.1 Prac. #7,9
UC #1-4