Unit 9: Application of Forces and Transfer of Energy Flashcards
What is a force (2pts)
What is a Force?
* A force is a push or a pull.
* The SI unit for force is newton (N).
Types of Forces
Contact Forces
definition + how many contact forces?
Contact Forces
* When an object is touched, contact forces act on it (there is physical contact between 2 surfaces).
- e.g. Friction, Elastic Force, Normal Force, Tension Force
There are 5 contact forces:
Friction
Elastic Force
Normal Force
Resultant Force
Applied Force
Types of Forces
Non-Contact Forces
definition + how many non-contact forces?
Non-Contact Forces
* A non-contact force is a force which acts on an object without coming physically in contact with it.
- e.g. Gravitational Force, Magnetic Force
There are 2 non-contact forces:
Gravitational Force
Magnetic Force
Contact Forces
Friction
(3pt)
Friction
* force that opposes motion between 2 surfaces in contact
* The mass of object and roughness of the surfaces in contact affects friction!
- When the object is heavier/lighter and when surface is smoother/rougher, the amount of friction produced increases/decreases.
Contact Forces
Applied Force (2pt)
Applied Force
* Force which is applied to an object by another object (literally).
* acts in the opposite direction of elastic and tension force.
- e.g. a man pushing a barrel; there is an applied force pushing the barrel
Contact Forces
Elastic Force (2pt)
Elastic Force
* force acting on a stretched or compressed elastic object to return to its original shape (e.g. springs)
* acts in the opposite direction of applied force
Contact Forces
Tension Force (2pt)
Tension Force
* Tension force is a contact force that occurs when an object is stretched.
* acts in the opposite direction of applied force
Contact Forces
Normal Force (2pt)
Normal Force
* Normal Force is defined as the force that a surface exerts on an object.
* The surfaces of the objects must be in contact with each other (perpendicular) and they balance gravitational force/other forces.
Non-contact Forces
Gravitational Force (1-2 impt pt)
Gravitational Force
* Force that attracts two objects towards each other.
* Gravity pulls things down.
* Gravity pulls things radically inwards.
* Note: Gravity is not the same as gravitational force!
- Gravitational Force is the acting force between two objects. On the other hand, gravity is the force occurring between an object and the very big object (Earth).
- Always use Gravitational Force (or weight) to answer qns!
- e.g. When Earth exerts a gravitational force on an object and pulls it towards its centre, the object has weight. (refer to weight vs mass section)
Non-contact Forces
Magnetic Force (1 impt pt, 4pts)
Magnetic Force
* Magnetic force is the push or pull between magnets only or magnets on magnetic materials.
* like poles of magnets facing each other = attraction
* unlike poles of magnets facing each other = repulsion
* magnetic materials (Cobalt, Iron, Nickel and Steel) can attract magnets (but not repel them).
How to measure force? (optional, 1pt)
How to Measure Force?
* Forces are measured with force-meters (e.g. spring balances).
* The SI unit of force is the newton (N).
* Equipment (spring balances) than can measure force (= N, weight)
* There are two types of spring balances:
- Compression spring balance (spring is compressed when a force acts on it.)
- Extension spring balance (spring stretches when a pulling force acts on it)
Formula for weight?
Weight = mass x acceleration due to gravity
W = mg
* Note: g is a constant known as the acceleration due to gravity & is taken to be ≈ 10 m/s²
- The weight of an object is the gravitational force acting on that object.
- Since weight is a force, it is related to the equation
- typically, 10N = 1kg = 1000g
- only need to know how to calculate weight!
- Weight is always linked to normal force (size of arrow drawn for diagrams must be same size in y3-y4)
Effects of a Force on Size and/or Shape of an object (3-4 impt pt)
- The transfer of energy between objects may cause changes in the size and/or shape of an object.
- e.g. moulding plasticine
- A force applied on an object can cause a turning effect about a fixed point called a pivot.
- As the Force increases, the turning effect increases.
- As the (perpendicular) Distance of the Force from the pivot increases, the turning effect increases.
- Examples of turning effect of forces include using a fishing rod, opening a door etc.
- (optional) *Formula for Turning Effect = Force x (perpendicular) distance from the pivot
Effort vs Pivot template answer (reason):
- The distance between the pivot and the force (state source of force) is greater/lesser, hence lesser/greater force is needed to create the turning effect to (purpose).
Load vs Pivot (force) template answer (reason):
- The distance between the pivot (source of force) and the weight of (item) is greater/lesser, hence there is greater/lesser turning effect to (purpose).
What is pressure? (3 pt)
Pressure
* Pressure is the force acting perpendicularly per unit area.
* The SI unit for pressure: Pascal (Pa)
* 1 Pa = 1 N/m²
- Pressure = Force / Area
Factors affecting Pressure
* Force
* Area
- When force increases/decreases, pressure increases/decreases.
- When area increases/decreases, pressure increases/decreases.
What are the factors affecting pressure?
Factors affecting Pressure
* Force
* Area
- When force increases/decreases, pressure increases/decreases.
- When area increases/decreases, pressure increases/decreases.
What is mass? (1-2pt)
- Mass = Amount of matter in an object (SI Unit = kg, remains constant regardless of location)
What is weight? (2-3pt)
- Weight = Gravitational Force exerted on an object (SI Unit = N, changes depending on location)
- Weight (N) = mass (m) x gravity (g, usually 10 m/s²)
- Weight (N) can sometimes equal to Force (N) (e.g. when a book is falling)
What is work done? (4pt, 5 subpt)
- Work Done (J) = Force (N) x distance (d)
- Work Done = the force multiplied by the distance moved in the direction of the force.
- Conditions that must be present for work to be done:
- There is a force acting on the object.
- The object moves through a distance.
- The movement of the object is in the direction of the force.
- No work is done when:
- Object does not move.
- Direction of force is not in the same direction of the movement.
Formula for work done?
- Work Done (J) = Force (N) x distance (d)
What are the conditions that must be present for work to be done?
- Conditions that must be present for work to be done:
- There is a force acting on the object.
- The object moves through a distance.
- The movement of the object is in the direction of the force.
No work is done when:
- No work is done when:
- Object does not move.
- Direction of force is not in the same direction of the movement.
What is Energy? (4pt, 3subpt)
Energy
* Energy is the ability to do work.
* Energy is transferred when work is done.
* Energy is measured in Joules (J).
* the amount of work done on an object is related to :
1. The energy transferred to the object
2. The force applied on the object
3. The distance travelled by the object
