Forces
How can friction be reduced?
Oil or grease on moving parts Using ball bearings Smooth surfaces e.g. road creates less friction and can use smooth tyres Rain - bicycle brakes don't work as well in the rain which acts as a lubricant
What is speed?
Speed is Distance over Time SIDOT
What is terminal velocity?
Terminal velocity is the constant speed reached when the forces of weight and air resistance are balanced when an object falls
What is Hooke's law?
The amount a spring stretches is directly proportional to force applied. Hookes law F= k x e where k is the spring constant (N/m) that depends to the material of the spring a; e is the extension ; F is the force
Gravitational force
The attractive force existing between any two objects that have mass On earth it is 10N/kg on the moon it is 1/6 less than on the earth as the moon is smaller
What happens when a spring is extended beyond the elastic limit?
The coil cannot recoil any longer after it is stretched beyond its elastic limit and will be permanently stretched
How can a lever increase the force applied?
The longer the lever the greater the turning force around the pivot
What is weight and what unit is it measured in?
The measure of the force of gravity on an object. Measured in Newtons WEIGHT =MASSxGRAVITY NB on earth weight=mass x 10 N/kg
What is a pivot?
The point around which a turning force (moment) happens
What does the arrow show in a force diagram?
The size and direction of the force
What is the resultant force?
The sum of all the forces acting on an object If forces are balanced the resultant force is zero
Draw the forces acting on a boat
Upthrust is buoyancy
How is a newton measured?
Using a Newtonmeter
How can air resistance be increased?
Using a parachute
What is water resistance?
Water resistance is the drag force of an object moving through water and is a form of friction
What is a balanced force?
When forces on an object are of EQUAL SIZE and OPPOSITE DIRECTION (so the resultant force is zero). If forces are balanced the object keeps on doing what it is doing: If the object is moving it continues to move at a constant speed with no acceleration If the object is stationary it does not move
What is an unbalanced force?
When forces on an object do not cancel out; The resultant force causes a change in speed or a change in direction
What are the stages of forces acting on a skydiver?
1. Gains speed as leaves plane as the weight is greater than the air resistance so the forces are unbalances and the sky diver falls more quickly 2. Steady speed ( terminal velocity) as forces are balanced when the weight is equal to air resistance 3. Losing speed as parachute opens which increases the air resistance making unbalanced forces 4. new steady speed ( terminal velocity) as air resistance with parachute is equal to the weight 5. no speed after landing when the weight is equal to the reaction force and the forces are balanced
How can you measure the stretching of a spring?
1. set up as shown 2. measure length of spring 3. add weight 4. measure new length 5. repeat with different weights 6. record in a table and plot a graph The extension is the difference between the original length of the spring and the stretched spring
What effects can a force have on an object?
1. speed up or start moving 2. slow down or stop 3. change direction eg hitting a ball with a bat 4. change shape e.g. squeezing a bottle 5. turn e.g. turning a spanner
How can you find the density of a regular object e.g. a cube?
1.Use a mass balance to find mass in g or kg 2. Calculate volume in cm² or m² Density =mass/volume
How can you find the density of an irregular object e.g. a marble?
1.Use a mass balance to find mass in g or kg 2. Calculate volume in cm² or m² by using a displacement of a known volume of water in a measuring cylinder Density =mass÷ volume
What is the density of water?
1g/cm² Note: salt water is more dense than water
Gina weighs 500M and stands 0.5m from a pivot on a sea saw what force does she exert?
250Nm
What type of non contact forces are there?
A force created when objects do not touch 1. Magnetism 2. Electromagnetic 3. Nuclear 4. Gravitational
What type of contact forces are there?
A force created when objects touch 1. Friction-Air resistance-Water resistance 2. buoyancy 3. Thrust 4. Push, pull, twist, turn or a squeeze
What is a force?
A force is a push or pull, a twist a turn or a squeeze
What is a reaction force?
A force that is equal and opposite e.g. to gravity
What is friction?
A force that opposes motion between two surfaces that are in contact eg more friction with a rough surface e.g. carpet or sandpaper and less friction on a smooth surface e.g. road
What is air resistance or drag?
A force that opposes motion though air and is a form of friction
What is a lever?
A lever is simple machine used to turn a small force into a larger force
What is mass and what unit is it measured in?
A measurement of how much matter is in an object Measured in kg NB it never changes so is the same on the moon as on earth
What is a moment?
A moment is a turning force around a pivot The moment or turning force can be increased by increasing the force or increasing the distance from the pivot Note the distance must be perpendicular
What is a lubricant?
A substance applied to reduce friction between 2 surfaces e.g. oil or grease to help them move more easily
What are the benefits and disadvantages of friction on a bicycle?
Advantages: It allows objects to stop e.g. bike tyres It allows tyres to grip the road so a bike can move forward- thick rubber tyres with a big tread have more friction It allows the brakes of a bicycle to work It allows the rider to hold the handlebars and feet to grip the pedals. Disadvantages Air resistance slows rider down and limits the maximal speed Friction between moving parts wastes energy and creates wear
How can you compare the density of liquids?
By allowing them to separate into layers in a graduated measuring cylinder
How can moments be balanced on a seesaw?
Clockwise moments=anticlockwise moments Clockwise force (N) x perpendicular distance (m) = anticlockwise force (N) x perpendicular distance (m)
How can you increase the pressure?
Decreasing the area eg a small area on the blade of a knife or on a drawing pin or a stiletto heel
What is density?
Density is mass per unit volume 1000g/cm² = 1kg/m²
How do 2 springs in parallel work?
Each spring extends half as much as a single spring would Total extension =extension of one spring ÷number of springs
How do 2 springs in series work?
Each spring extends the same amount as one spring would Total extension= extension x number of springs so total extension=2 x extension of one spring
How can air resistance be reduced?
Eg car or cycle helmet streamlined shape
What is pressure?
Force per unit area
How can you decrease the pressure?
Increasing the area e.g. skis decrease the pressure by increasing the area on which the skier can walk over snow
What happens to the force on a spring when a spring is extended twice as far?
It doubles
What is the unit of a Force?
Newton (N)
What is pressure measured in?
1 Newton per 1 m² = 1 Pascal (pa)
