8B Forces Flashcards
State two examples of contact forces.
Friction, air resistance, tension, normal contact force, and Upthrust
State two examples of non-contact forces.
Magnetism, gravity, and electrostatic force.
What is resultant force?
The overall force acting on an object.
What do the arrows on a free body diagram show us?
The direction of the forces acting on an object.
What are balanced forces?
Forces equal in size, acting in opposite directions.
Define equilibrium.
The forces acting on an object are balanced.
Describe the effect of zero resultant force on a stationary object.
It remains stationary
Describe the effect of zero resultant force on a moving object.
It remains at a constant speed.
Define what a frictional force is.
A force that acts in the opposite direction to the movement of an object.
What is drag?
A frictional force where one of the surfaces is a fluid (a liquid or gas).
Give an example of useful frictional force.
Friction between tyres and breaks.
Give an example of unhelpful frictional force.
Air resistance on moving objects
What is streamlining?
Changing the shape of an object to reduce drag.
Describe how penguins are streamlined to swim through the water.
The penguin has a specific shape that means it moves through the water easily.
Describe how cyclists reduce drag during races.
They have streamlined helmets and crouch low to reduce drag.
Why is it useful for racing cars to be streamlined?
So that they can move faster.
Define deformation.
When something changes shape.
What is the difference between elastic and inelastic deformation?
Elastic- an object returns to its original shape after a force is removed, inelastic does not.
How does compression affect an object?
Squashes it.
How does tension affect an object?
Stretches it.
Describe how force and extension are directly proportional for springs.
When an increasing force is applied, the extension increases at the same rate.
What does spring constant tell us about an object?
How much force it would take a spring to stretch a certain distance.
Give one use for elastic materials.
Sports clothing
Give one use for brittle materials.
Building materials.
What is an elastic material?
When an object is deformed by returns to its original shape when the force is removed.
What equipment is required when investigating the elasticity of a material?
Clamp and retort stand, ruler, weights, spring and weight holder.
What happens if an object is stretched beyond its elastic limit?
It does not return to its original shape.
State Hooke’s Law.
The force applied to a spring is directly proportional to its extension.
What graph can be plotted when investigating the elasticity of a material?
Force against extension.
How can spring extension be calculated?
Extended spring length – initial spring length.
State the equation which links spring constant, force and extension.
Spring constant = Force ÷ Extension
What are the units of measurement for spring constant, force and extension?
Spring constant (N/m), Force (N) and Extension(m)
What is the independent variable for testing Hooke’s Law?
Number of masses added.
How will you convert the length of the spring from mm into metres?
Divide by 1000
How do you calculate extension?
Subtract the initial length from the new length when weights are added.
What force is equal to a 100g mass?
1N
What is the initial force acting on the spring?
0N
How will you calculate the spring extension of each material?
Spring extension = force ÷ extension.
What is a line of best fit?
A line that goes through most points, but is not a dot to dot.
How do you draw a line of best fit?
Draw a line that goes through most of the points.
What is the limit of proportionality?
The point after which the extension is not directly proportional to force.
What is pressure?
A force exerted over a certain area.
What are the units of measurement for pressure?
Pascals (Pa) or N/m2
State the two factors which determine pressure exerted by an object.
Force/ weight and area
Give an example of a situation where pressure is high.
Treading on a single nail.
Give an example of a situation where pressure is low.
Lying on a bed of nails.
Why do high heels and flat shoes exert different pressures?
They have a smaller area touching the floor.
State the equation which links pressure, force and area.
Pressure = Force ÷ Area
When calculating pressure, what could be used instead of force?
Weight
What causes liquid and gas pressure?
Particles colliding with a surface.
What does liquid or gas pressure depend on?
Depth and altitude.
Why don’t we normally notice pressure on our bodies?
Pressure inside and outside our bodies is equal.
State how pressure changes with depth in a liquid.
Pressure increases with depth in a liquid.
Why does pressure change as you go deeper in a liquid?
The number of liquid particles above something increases and the force of gravity pulling these particles down also increases.
State how pressure changes with altitude in a gas.
Pressure decreases with altitude.
Why are there fewer air particles as you increase in altitude?
Gravity is weaker higher up.
How do airplanes compensate for a drop in pressure outside?
As you increase your altitude, the pressure in the cabin decreases slightly.
Define density.
The mass of a material in a particular volume, measured in kg/m3.
What determines whether an object floats or sinks in water?
Its density in comparison to water.
What is buoyancy?
An upward force on an object in a liquid.
What happens when objects are placed in water?
Weight pulls it down and Upthrust pushes it upwards.
What is the upward force of water acting on an object?
Upthrust
How can we find the upward force of water acting on an object?
Find the volume of water displaced by the object
How are large ships able to float, despite having a large mass?
They have a greater weight, so a greater force of Upthrust acts on them.
Who first developed the theory of buoyancy?
Archimedes
