Forces

What are scalar quantities

These are quantities that only have magnitude

What are vector quantities

These are quantities that have magnitude and direction

Explain why reaction time affects thinking distance of a car

• distance = speed x time

• So longer reaction time= longer distance

Examples of scalar quantities

• distance

• Speed

• Mass

• Energy

• Volume

• Density

• Power

Examples of vector quantities

• Displacement

• Velocity

• Weight

• Force

• Acceleration

• Momentum

What is a force

This is a push or pull that acts on a object due to an interaction with another object

How does force affect an object

• changes speed

• Changes shape

• Changes direction

What is weight

This is the amount of gravity acting on an object

What is electrostatic force

This is the force between two charged objects

What is thrust

The force causing an object to move

What is air resistance (drag)

The friction of the air on a moving object

What is upthrusr

The force of a fluid pushing a liquid upwards making it to float

What is compression

A force that acts inward on an object squeezing it

What is tension

This is a force transmitted by a string when pulled upon by forces acting on its opposite ends

What is reaction force

This is a force due a contact between two objects

What are the types of forces

• contact

• Non contact

What is a contact force

A force that acts between two objects physically touching

Examples of contact forces

• friction

• Tension

• Reaction force

What is a non contact force

This a force that acts at a distance without any contact between bodies due to the action of a field

Examples of non contact forces

• gravitational attraction

• Electrostatic

• Magnetic

What is weight

This a force acting on an object due to gravitational attraction

What are the importances of weight

• objects stay firmly on the ground

• Objects always fall to the ground

• Keeps satellites in orbit

What is mass

This is the amount of matter in an object

What is Centre of mass

The point through the weight of an object acts

What is a resultant force

This is the addition of all the forces acting on an object

What does resultant force determine

• the direction thr object will move in

• The magnitude of the final force experienced by the object

What are balanced firces

This means that the forces acting on a object have combined in a way that they cancel each other and there’s no resultant

What are unbalanced forces

This means the forces acting on an object combine is such a way they don’t cancel each other out completely and there is a resultant force

What is normal contact force

The forces arising when an object rests against another object acting at a 90 angle to the plane of contact

What is work done

This is when an object is moved over a distance by a force applied in the direction of its displacement

What happens when a force acts in the opposite direction of an objects movement

The object will lose energy

What happens when a force acts in the direction of an objects movement

The object gains energy

What is friction

This is a force that opposes the motion of an object

What happens when friction is present

Energy is transferred by heating this raises the temperature and energy is transferred to the thermal store of the object and its surroundings

What is stretching

These are forces in opposite directions away from the object

What is bending

These are forces that distort the object

What is compressing

Forces in the opposite direction towards the object

When an object is compressed what forces are acting

• weight of the mass

• Reaction force from the surface to the spring

  they act towards each other

What forces are acting on a stretched object

• The weight of the mass

• The tension in the spring

  they act away from each other

What forces are acting on a bent object

• weight of the mass

• Reaction force

What is deformation

This is a change of shape

What are the types of deformation

• elastic

• Inelastic

What is elastic deformation

When an object returns go the original shape when the stretching force is removed e.g rubber bands, fabrics, steel springs

What is inelasic deformation

This is when objects remain stretched and do not return to their original shape when the stretching force is removed e.g plastic clay glass

What is hookes law

The extension of an object is directly proportional to the force applied up to the limit of proportionality

What does spring constant show

The higher the spring constant the stiffer the object

What is elastic potential energy

The energy stored in an elastic object when work is done on it

Required practical

What are the possible systematic errors when measuring extension

• make sure measurements are taken at eye level to avoid parallax error

What are random errors in measuring extension

The accuracy of an experiment is reduced if there is no pointer

What are the safetY considerations when measuring extension

• wear goggles in case spring snaps

• Stand up during experiment to make sure no feet are directly under the mass

• Place a mat below the masses to prevent any damage in case they fall

• Use a G clamp to secure the clamp stand to the desk so that the clamp and masses do not fall over

What is a couple

These are two forces that are equal and opposite which act on an object without passing through the same point

What is a moment

This is the turning effect of a force about a pivot

M=F x D

Why is the door handle place on the opposite side of the hinge

This means for a given force the perpendicular distance from the pivot is larger this creates a larger moment making it easier to open the door

What is the principle of moments

If an object is balanced the total clockwise moment about a pivot equals the total anticlockwise moment about that pivot

What is pressure

This is the force per unit area

What is the formula for pressure in a liquid

P= h x p x g

P= pressure

H= height

p= density of the liquid in kg/m cubed

g= gravitational field strength

What is upthrust

This is a force that pushes upwards on an object submerged in a fluid

How does upthrust affect sinking

If the upthrust of an object is greater than its weight it will float and if it is lower it will sink

How does density affect sinking

If the density of the object is less than the density of the fluid it is immersed in it will float and if it is higher it will sink

Why will an object sink if it’s density is greater than the fluid it is in

This is because if the density of the object is greater than the fluid the object can never displace enough fluid to create an upthrust that will hold its weight up

What is distance

This is a measure of how far an object travels

What is displacement

This is a measure of how far something is from its starting point along with its direction

What is speed

This is the distance an object travels every second

What is acceleration

This is the rate of change of velocity

What information do velocity time graphs show

• if an object is moving at constant acceleration or deceleration

• The magnitude of acceleration or deceleration

What is Newton’s first law of motion

Objects will remain at rest or move at constant velocity unless acted on by a resultant force

What is Newton’s second law

The acceleration of an object is proportional to the resultant force acting on it and inversely proportional to the objects mass

What is Newton’s third law

When two bodies interact the forces they exert on each other are equal and opposite

What is inertia

This is the tendency of an object to continue in its state of rest or uniform action unless acted upon by an external force

What is the formula for inertial mass

Inertial mass = mass/acceleration

What is the relationship between inertial masses and acceleration

The larger the inertial masses the smaller the accelerations and vice versa

What is the stopping distance of a car

This is the total distance travelled during the time it takes for a car to stop in response to an emergency

Formula for stopping distance

Stopping distance = thinking distance + braking distance

What is thinking distance

The distance travelled by a car from when a driver realizes they need to break to when they apply the brakes

What is braking distance

The distance travelled under the breaking force

What is the formula for reaction distance

Reaction distance= speed of the car x drivers reaction time

What factors affect thinking distance

• speed

• Tiredness

• Distractions

• Intoxication

What factors affect breaking distance

• vehicle condition

• Road condition

• Vehicle mass

What is the work done by brakes when a vehicle slows down to a halt

Breaking force x breaking distance = kinetic energy

What is the formula for momentum

p=mv

When does momentum change

• the object accelerates or decelerates

• The object changes direction

• The mass of the object changes

What is momentum in a closed system

The total momentum before an event is equal to the total momentum after the event

What are the types of collisions

• elastic

• In elastic

What is an elastic collision

This is where objects collide and move in opposite directions

What is inelastic collision

This is when objects collide and move in the same direction together

What is the formula for force in termd of momentum

Change in momentum / change in time

What are the safety precautions in cars

• seat belts

• Air bags

• Crumple zones

Required practical: how does force affect acceleration

Required practical: how does mass affect acceleration

What are the systematic errors when considering effect of force

• Ensure any weights removed from the weight hanger are transferred to the toy car or troller to ensure the total mass of the system remains constant

What are the random errors when considering effect of force and mass on acceleration

• Inaccurate measurement of time ensure to take repeat readings when timing intervals and calculate an average to keep error yo a minimum

• Start the toy car by releasing it allowing it to accelerate under the force of the weights attached to the string ensure not to give a push

What is friction

The resistance an object encounters when moving over a solid or through a fluid

Why do cars have maximum speed

• there is a maximum forward force as the speed of the car increases air resistance increases until the air resistance is equal in size to forward force so the car can no longer accelerate

Why do hailstones reach terminal velocity

Why does temp of brakes increase as they are used

• work is done due to friction

• This causes an increase in the internal energy of brakes

How does a bumper reduce damage during collision

• Increases the time taken to stop during the collisions

• So the rate of change of momentum decreases

• Reducing the force on the people