2026 Unit 2 - Physics - Types of Forces

Force: A force is a push or pull 

Contact force: A force that requires contact to act on the object. 

Non-Contact force: A force that acts on an object without physically touching it 

  

Types of Contact forces: 

- Frictional force 

- Spring force 

- Tension force 

- Air resistance 

- Normal force 

- Applied force 

  

Types of non-contact forces: 

- Electrical force 

- Magnetic force 

- Gravitational force 

  

Balanced force: A balanced force is equal in size and opposite in direction. When forces are balanced, there is no change in motion. The net force is 0N. 

Unbalanced force: An unbalanced force is when forces applied to an object in opposite directions are not equal in size. Unbalanced forces result in a change of motion. The net force is not 0N.  

  

Weight: The gravitational force with which the Earth attracts the masses towards its center.  

Net Force: The sum of all forces acting on an object. Eg. 5N right, 0N (balanced force) 

 

Work 

  • Work is Motion caused by a force. 

  • Work = Force x Distance 

  • [Work done (Measured in J – Joules) = Force (Measured in N – Newtons) x Distance (Measured in M – Metres)] 

  • If the object doesn't move, then no work was done. 

 

Simple Machine: A mechanical device that changes the direction or magnitude of a force. 

Types of Simple Machines: 

  • Lever 

  • Inclined Plane 

  • Wedge 

  • Wheel and Axle 

  • Pulley 

  • Screw 

Inclined Plane:  

  • A flat supporting surface, tilted at an angle, with one end higher than the other. 

  • An inclined plane can be used to raise or lower a heavy object. It takes less force to move a heavy object up a ramp, but the object has to be moved a greater distance. A gentle slope means less force needed but more distance will be covered. A steep slope means more force needed but a shorter distance covered.  

Wedge: 

  • A simple machine that changes either the magnitude (size) or direction of a force 

  • A triangular tool, often made of metal, wood, stone or plastic. 

  • It is thick on one end and tapers to a thin or sharp edge on the other end.  

  • A wedge may be attached to a handle to make it easier to use. 

  • Used to cut, split, tighten and hold back, hold together or to scrape.  

Lever: 

  • A stiff bar that moves about a fixed point, allowing you to gain a mechanical advantage in moving an object or in applying a force to an object. 

Parts of a Lever: 

  • Fulcrum: the support or turning point of a lever 

  • Load: the object to be moved 

  • Effort: the applied force acting on the lever 

Types of Levers: 

  • 1st class levers: the Fulcrum in the middle. Eg. Seesaw, scissors, crow-bar 

  • 2nd class levers: the Load in the middle. Eg. Wheelbarrow, nutcracker 

  • 3rd class levers: the Effort in the middle. Eg. Stapler, tweezers.  

Use for Levers: 

  • Increasing applied force: 1st or 2nd class levers 

  • Increasing distance moved: 1st or 3rd class levers 

  • Increasing speed of object: 1st or 3rd class levers 

 

Mechanical Advantage (MA): A way of making work easier by using tools or machines. The factor by which a machine multiplies the force.  

Calculations using force: 

  • MA = Output force / Input force 

  • MA = Resistance force / Effort force 

Lever Arms: 

  • MA = Input arm distance / Output arm distance 

  • MA = Length of effort arm / Length of load arm 

Inclined planes:  

  • MA = Ramp Length / Ramp Height 

 

Buoyancy: The tendency of an object to float or to rise in a fluid when submerged. This fluid can be either a liquid or gas.  

Floating: An object floats when the weight force on the object is balanced by the upward push of the water on the object.  

Sinking: If the weight force down is larger than the upward push of the water on the object then the object will sink.  

Density: The quantity of something per unit volume, unit area or unit length.  

If an object is less dense than the liquid, it means that the object's molecules are spaced out more than the molecules in the liquid, so it can't sink. The buoyant force is strong enough to keep it on the surface, and it floats.  

If an object is denser than the liquid, it means the object's molecules are tightly packed, and the buoyant for isn't strong enough to keep it afloat, so the object sinks.  

Big ships float because even though they are heavy, they also contain a lot of air (which has low density). The weight of the ship and air pushing down is less than the upwards force from buoyancy, so they can float.  

 

Archimedes' Principle: "The buoyant force is equal to the weight of the displaced water." 

 

Friction: A contact force that resists or stops motion when two surfaces rub against each other.  

Drag: A force that opposes an object's motion. It's essentially the resistance experienced by an object as it moves through a fluid.  

The amount of friction depends on the force pushing the surfaces together. If this force increases, the hills and valleys of the surfaces can come into closer contact. The close contact increases the friction between surfaces. Objects that weigh less exert less downward force than objects that weight more.  

Advantages of Friction: 

  • Required to enable us to push against the ground and walk.  

  • Allows a car’s tires to push against the ground to move the car. 

  • Friction is in brakes allows the car to slow down 

Disadvantages of Friction:  

  • Extra energy is needed to overcome friction 

  • Can heat up parts  

  • Can cause wear 

Increasing Friction 

  • Making surfaces rougher 

  • Increase the force pushing the surfaces together 

Reducing Friction 

  • Use lubricants, such as motor oil, wax, grease, water 

  • Ball bearings 

 

Distance:  

  • How far something travels. 

  • Tells you the length of the path between two points.  

  • Measured in metres (m) 

Time: 

  • How long something takes to happen 

  • Measured in seconds (s), minutes (mins), or hours (h) 

Speed: 

  • How fast something moves 

  • How much distance is covered in a certain amount of time.  

  • Speed = Distance ÷ Time 

  • Measured in metres per second (m/s) or kilometres per hour (km/h) 

Velocity: 

  • How fast something is moving and the direction it is moving in. 

  • Velocity is measured in the same units as speed, such as metres per second (m/s) or kilometres per hour (km/h), but it always includes a direction 

Acceleration:  

  • How quickly an object’s velocity changes. If something speeds up, slows down, or changes direction, it is accelerating. 

  • Commonly measured as a change in speed per second, or “metres per second, per second.”.  

  • Written as metres per second squared, or m/s/s 

 

Newton's 1st Law of Motion – Law of Inertia 

"An object at rest, or in motion, will stay at rest, or in motion, unless acted upon by an outside, unbalanced force." 

Newton's 2nd Law of Motion – Law of Acceleration 

"Acceleration is produced when a force acts on a mass. The greater the mass (of the object being accelerated) the greater the amount of force needed (to accelerate the object)." 

Force = Mass x Acceleration 

Newton's 3rd Law of Motion – Law of Action and Reaction 

"For every action, there is an equal and opposite reaction."