Knowt
Forces and their Effects
Forces and their Effects
A force is either a push or a pull that one object exerts on another object. It can produce, slow down, speed up or stop motion or change its direction.
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Types of forces
Contact Forces:
Forces that result from direct physical contact between objects, such as friction, tension, air resistance and normal contact forces
Friction:
Frictional force arises when two surfaces are in contact and resist relative motion.
Types:
Static Friction: Acts between stationary surfaces.
Kinetic Friction: Acts between moving surfaces.
Tension:
Tension:
Tension is the pulling force transmitted through a string, rope, cable, or any similar object when it is pulled tight by forces acting from opposite ends.
Example: Tension in a rope supporting a hanging object or in a cable supporting a bridge.
Normal Force:
Normal force is the force exerted by a surface that supports an object in contact with it, perpendicular to the surface.
Example: The ground supporting the weight of an object placed on it exerts a normal force upward.
Air Resistance:
Air resistance is a frictional force acting on an object moving through the air.
Example: When a parachute descends or a ball moves through the air, air resistance opposes the motion.
Non-contact Forces: Forces that act at a distance, including gravitational, electrostatic,nuclear and magnetic forces.
Gravitational Force:
The force of attraction between any two masses in the universe.
Example: The gravitational force between the Earth and objects on its surface, causing objects to fall towards the ground.
Electrostatic Force:
The force between electrically charged objects.
Example: The attraction or repulsion between charged particles, like the force between protons and electrons within an atom.
Magnetic Force:
The force exerted between magnets or between a magnet and a magnetic material.
Example: The force that causes magnets to attract or repel each other, or the force exerted on a magnetic material in a magnetic field.
Nuclear Forces (Weak and Strong):
Forces that act within the nucleus of an atom.
Examples:
Strong Nuclear Force: Binds protons and neutrons together within the nucleus.
Weak Nuclear Force: Involved in processes like radioactive decay.
Newton’s laws of motion
Newton's 1st Law
Every object will continue in its state of rest or uniform motion in a straight line unless a resultant force acts on it.
Newton's 2nd Law
When a resultant force acts on an object of a constant mass, the object will accelerate in the direction of the resultant force. The product of the mass and acceleration of the object gives the resultant force.
Force= mass x acceleration
Newton's 3rd Law
Every action has an equal and opposite reaction.A force is either a push or a pull that one object exerts on another object. It can produce, slow down, speed up or stop motion or change its direction.
F₁=F₂
mass₁ x acceleration₁ = mass₂ x acceleration₂
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Vectors
In vector diagrams, vector quantities such as forces are represented by an arrow.
❂ The length of the arrow is proportional to the size of the force.
❂ The direction of the arrow shows the direction of the force.
Drawing vectors
Step 1: choose an appropriate scale
Step 2: measure the required angle using a protractor from the baseline/second force.
Step 3: draw an arrow of length proportional to the force using the scale taken.
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Adding vectors
Parallel vectors
If they are in the same direction, they will be added.
If they are in opposite directions, the resultant will be in the direction of the greater force and its size will be the difference of the two vectors.
If they are equal and opposite, there will be no resultant force.
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Non-Parallel vectors
Tip To Tail Method
Redraw one of the vectors, placing the tail of the vector at the tip of the second vector. Join the two corners to get the resultant force.
Parallelogram Method
Complete the parallelogram, the diagonal of the parallelogram will be the resultant.
Centre of Mass and Stability
The center of mass of an object is the point at which the weight of the object acts. For symmetrical objects, the center of mass is at the point of intersection of its symmetries
When an object is suspended, its center of mass will come below it. To find the center of mass of a lamina, it is suspended from a point and a plumb line is hung next to it.
A line is drawn using a pencil along the plumb line. This is repeated from multiple points, the point of intersection of the lines is the center of mass
An object is stable when its center of mass is above its base. If the center of mass is not directly above its base, the object will topple over
The lower the center of mass of an object, the greater the stability
The greater the base area of an object, the greater the stability
Moments
Pivot: a joint about which rotation happens
Moment: turning effect of a force about a point
SI unit: Newton metres (Nm)
Moment = force x perpendicular distance from pivot
moment ∝ perpendicular distance
the perpendicular distance must be at a right angle to the direction of force
Everyday examples: scissors, wheelbarrow, lever, spanners
Principle of moments:
For an object in equilibrium, sum of clockwise moments = sum of anticlockwise moments so the net (resultant) moment becomes 0
The sum of forces in one direction must equal the sum of forces in the opp. Direction
Levers
A lever is a simple machine consisting of a rigid bar (lever arm) that pivots around a fixed point called the fulcrum.
Types of Levers:
First-class lever:
Fulcrum between the effort and the load.
Examples: seesaw, crowbar.
Second-class lever:
Load between the fulcrum and the effort.
Example: wheelbarrow.
Third-class lever:
Effort between the fulcrum and the load.
Example: forearm when lifting a weight.
Gears
Gears are toothed wheels that transmit rotational motion and torque from one part of a machine to another.
Types of Gears:
Spur Gears:
Straight teeth parallel to the axis of rotation.
Commonly used in mechanisms requiring speed and torque transfer.
Helical Gears:
Teeth are angled to the axis in a helix shape.
Provide smoother and quieter operation compared to spur gears.
Bevel Gears:
Teeth are cut on a cone-shaped surface.
Used to transmit motion between intersecting shafts.
Worm Gears:
Consist of a screw (worm) and a wheel (worm gear).
Provide high reduction ratios in a compact space.
Key Concepts:
Gear Ratio:
Ratio of the number of teeth on the driven gear to the number of teeth on the driving gear.
Determines the relationship between rotational speeds and torques.
Velocity Ratio:
Ratio of the rotational speed of the driving gear to the rotational speed of the driven gear.
Directly related to the gear ratio but includes consideration of rotational speed
Forces and their Effects
Forces and their Effects
A force is either a push or a pull that one object exerts on another object. It can produce, slow down, speed up or stop motion or change its direction.
⠀
Types of forces
Contact Forces:
Forces that result from direct physical contact between objects, such as friction, tension, air resistance and normal contact forces
Friction:
Frictional force arises when two surfaces are in contact and resist relative motion.
Types:
Static Friction: Acts between stationary surfaces.
Kinetic Friction: Acts between moving surfaces.
Tension:
Tension:
Tension is the pulling force transmitted through a string, rope, cable, or any similar object when it is pulled tight by forces acting from opposite ends.
Example: Tension in a rope supporting a hanging object or in a cable supporting a bridge.
Normal Force:
Normal force is the force exerted by a surface that supports an object in contact with it, perpendicular to the surface.
Example: The ground supporting the weight of an object placed on it exerts a normal force upward.
Air Resistance:
Air resistance is a frictional force acting on an object moving through the air.
Example: When a parachute descends or a ball moves through the air, air resistance opposes the motion.
Non-contact Forces: Forces that act at a distance, including gravitational, electrostatic,nuclear and magnetic forces.
Gravitational Force:
The force of attraction between any two masses in the universe.
Example: The gravitational force between the Earth and objects on its surface, causing objects to fall towards the ground.
Electrostatic Force:
The force between electrically charged objects.
Example: The attraction or repulsion between charged particles, like the force between protons and electrons within an atom.
Magnetic Force:
The force exerted between magnets or between a magnet and a magnetic material.
Example: The force that causes magnets to attract or repel each other, or the force exerted on a magnetic material in a magnetic field.
Nuclear Forces (Weak and Strong):
Forces that act within the nucleus of an atom.
Examples:
Strong Nuclear Force: Binds protons and neutrons together within the nucleus.
Weak Nuclear Force: Involved in processes like radioactive decay.
Newton’s laws of motion
Newton's 1st Law
Every object will continue in its state of rest or uniform motion in a straight line unless a resultant force acts on it.
Newton's 2nd Law
When a resultant force acts on an object of a constant mass, the object will accelerate in the direction of the resultant force. The product of the mass and acceleration of the object gives the resultant force.
Force= mass x acceleration
Newton's 3rd Law
Every action has an equal and opposite reaction.A force is either a push or a pull that one object exerts on another object. It can produce, slow down, speed up or stop motion or change its direction.
F₁=F₂
mass₁ x acceleration₁ = mass₂ x acceleration₂
⠀
⠀
Vectors
In vector diagrams, vector quantities such as forces are represented by an arrow.
❂ The length of the arrow is proportional to the size of the force.
❂ The direction of the arrow shows the direction of the force.
Drawing vectors
Step 1: choose an appropriate scale
Step 2: measure the required angle using a protractor from the baseline/second force.
Step 3: draw an arrow of length proportional to the force using the scale taken.
⠀
Adding vectors
Parallel vectors
If they are in the same direction, they will be added.
If they are in opposite directions, the resultant will be in the direction of the greater force and its size will be the difference of the two vectors.
If they are equal and opposite, there will be no resultant force.
⠀
Non-Parallel vectors
Tip To Tail Method
Redraw one of the vectors, placing the tail of the vector at the tip of the second vector. Join the two corners to get the resultant force.
Parallelogram Method
Complete the parallelogram, the diagonal of the parallelogram will be the resultant.
Centre of Mass and Stability
The center of mass of an object is the point at which the weight of the object acts. For symmetrical objects, the center of mass is at the point of intersection of its symmetries
When an object is suspended, its center of mass will come below it. To find the center of mass of a lamina, it is suspended from a point and a plumb line is hung next to it.
A line is drawn using a pencil along the plumb line. This is repeated from multiple points, the point of intersection of the lines is the center of mass
An object is stable when its center of mass is above its base. If the center of mass is not directly above its base, the object will topple over
The lower the center of mass of an object, the greater the stability
The greater the base area of an object, the greater the stability
Moments
Pivot: a joint about which rotation happens
Moment: turning effect of a force about a point
SI unit: Newton metres (Nm)
Moment = force x perpendicular distance from pivot
moment ∝ perpendicular distance
the perpendicular distance must be at a right angle to the direction of force
Everyday examples: scissors, wheelbarrow, lever, spanners
Principle of moments:
For an object in equilibrium, sum of clockwise moments = sum of anticlockwise moments so the net (resultant) moment becomes 0
The sum of forces in one direction must equal the sum of forces in the opp. Direction
Levers
A lever is a simple machine consisting of a rigid bar (lever arm) that pivots around a fixed point called the fulcrum.
Types of Levers:
First-class lever:
Fulcrum between the effort and the load.
Examples: seesaw, crowbar.
Second-class lever:
Load between the fulcrum and the effort.
Example: wheelbarrow.
Third-class lever:
Effort between the fulcrum and the load.
Example: forearm when lifting a weight.
Gears
Gears are toothed wheels that transmit rotational motion and torque from one part of a machine to another.
Types of Gears:
Spur Gears:
Straight teeth parallel to the axis of rotation.
Commonly used in mechanisms requiring speed and torque transfer.
Helical Gears:
Teeth are angled to the axis in a helix shape.
Provide smoother and quieter operation compared to spur gears.
Bevel Gears:
Teeth are cut on a cone-shaped surface.
Used to transmit motion between intersecting shafts.
Worm Gears:
Consist of a screw (worm) and a wheel (worm gear).
Provide high reduction ratios in a compact space.
Key Concepts:
Gear Ratio:
Ratio of the number of teeth on the driven gear to the number of teeth on the driving gear.
Determines the relationship between rotational speeds and torques.
Velocity Ratio:
Ratio of the rotational speed of the driving gear to the rotational speed of the driven gear.
Directly related to the gear ratio but includes consideration of rotational speed
