Forces and Motion

explain what is meant by a scalar quantity. give 2 examples

a scalar quantity is a magnitude only. it can be described fully with a single numerical value e.g. distance, speed, time, mass, energy

explain what is meant by a vector quantity. give 2 examples

a vector quantity has both a magnitude and a direction e.g. force, velocity, displacement, momentum

which property of a distance-time graph can be used to calculate speed

gradient or slope

for the d-t graphs given below, decide which one is at a rest, which one is moving with a constant speed and which one is accelerating

• a = constant speed

• b = at a rest

• c = accelerating

what is meant by acceleration? give its unit

acceleration is the change in velocity per unit of time. unit = m/s²

which property of a v-t graph can be used to calculate acceleration

gradient(slope)

which property of v-t graph can be used to calculate distance travelled

area under the graph

identify the types of forces acting on the objects

A = Weight

B = Air resistance

name 2 types of forces that always opposes motion

1. friction

2. air resistance (drag)

a) which type of force holds planets around the sun?

b) which type of force holds electrons around nucleus

a) gravitational force

b) electrostatic force

state the ways that a force can afect the body that it is being applied on

• it can change the shape of the object (extension/compression)

• it can change the speed of the object

• it can change the direction the object is moving

state factors that affect the stopping distance

• reaction time

• initial speed

• road conditions

• tire conditions

• weather conditions

• driver’s conditions

• mass of the car

state 2 factors that affect the air resistance acting on a falling object

• surface area

• speed

describe how a falling object reaches to terminal velocity

at first object falls under the effect of its weight accelerating with g. as it accelerates, air resistance opposing the motion increases therefore resultant force acting on the object decreases and since F=ma, acceleration decreases.

when air resistance becomes equal to weight, forces are baalnced so resultant force = 0 therefore a = 0 and object reaches to terminal velocity

state hooke’s law

extension is durectly proportional to the force applied

explain what is the difference between elastic and plastic behaviour

in elastic behaviour, object recovers its original shape when the forces causing the extension is removed

in plastic behaviour, there is a permanent deformation to the shape of the object

what is the Newton’s first law

if a stationary object’s resultant force is zero, the object will remain stationary. if a moving object’s resultant force is zero, the object will continue to move at a constant velocity (same speed and direction)

what is the Newton’s second law

an object’s acceleration is directly proportional to the resultant force acting on it, and inversely proportional to the object’s mass

what is the Newton’s third law

the forces that two objects exert on each other when they interact are equal and opposite

what is terminal velocity

the maximum velocity an object can reach when falling through a fluid. it occurs when the resistive forces equal the object’s weight

what is elastic limit

the force beyond which an object will no longer deform elastically, and will instead deform plastically

what are the types of forces

• gravitational force (weight)

• reaction force = when an object rests on a surface, the surface exerts a push force on the object

• friction = occur when two surfaces move over one another (always oppose the motion of an object, causing it to slow down)

• drag = type of frictional force that occurs when an object moves through a fluid (a gas or a liquid). the particles in the fluid collide with the object moving through it and slow its motion

• air resistance = specific type of drag force and is therefore also a frictional force ( occurs when particles of air collide with an object moving through it and slows its motion

• thrust = force produced by an engine that speeds up the motion of an object

• upthrust = when an object is fully or partially submerged in a fluid, the fluid exerts an upward-acting push force on the object

• electrostatic = force between two objects with charge

  • Like charges repel one another, and opposite charges attract one another

  • When an electron gets close to a positively charged ion, the ion exerts a pull force on the electron (attraction)

  • When an electron gets close to another electron, the electrons experience a push force from one another (repulsion)

• magnetic = force between objects with magnetic poles

  • Like poles repel one another, opposite poles attract one another

  • When a north pole gets close to a south pole, they experience a pull force from one another (attraction)

  • When a north pole gets close to a north pole, they experience a push force from one another (repulsion)

• tension = occurs in an object (like a rope or spring) that is stretched. When a pull force is exerted on each end of an object, tension acts across the length of the object

what is thinking distance

the distance travelled in the time it takes the driver to react to an emergency and prepare to stop

what is reaction time

a measure of how much time passes between seeing something and reating to it

braking distance

the distance travelled under the braking force in metres (m)

state factors that affect the reaction time

• tiredness

• distractions (using a mobile phone)

• intoxication (alcohol or drugs)