Non-Contact Forces
Non-Contact Forces
- A non-contact force is defined as:
A force which acts at a distance, without any physical contact between bodies, due to the action of a field
- Examples of non-contact forces include:
- Gravitational force, Fg
- Electrostatic force, Fe
- Magnetic force, Fm
Gravitational force:
- The attractive force experienced by two objects with mass in a gravitational field e.g the force between a planet and a comet
- Weight, on Earth, is the gravitational force of the Earth acting on an object with mass
- Weight, on Earth, is the gravitational force of the Earth acting on an object with mass
- Electrostatic force:
- A force experienced by charged objects in an electric field which can be attractive or repulsive e.g. the attraction between a proton and an electron
- Magnetic force:
- A force experienced between magnetic poles in a magnetic field that can be attractive or repulsive e.g. the attraction between the north and south poles of magnets
Examples of non-contact forces
Worked example
A child drags a sledge behind them as they climb up a hill.
Describe the contact and non-contact forces acting on the child and the sledge.
Answer:
Step 1: Identify the contact forces acting on the child and the sledge
- The child pulls on one end of the rope and the sledge pulls on the other end of the rope
- This force is tension
- The ground pushes against the child and the sledge
- This is the normal contact force
- The surface of the sledge moves over the the surface of the ground opposing the motion of the sledge
- This force is friction
- The surfaces of the child's shoes move over the surface of the ground (enabling the child to walk)
- This force is also friction
- The child and the sledge move through the air
- This force is air resistance
Step 2: Identify the non-contact forces acting on the child and the sledge
- The gravitational pull of the Earth acts on the child and the sledge
- This force is weight