P2- Forces Flashcards
What does a scalar have?
Scalar quantities only have a magnitude and do not have a direction.
What does a vectors have?
Vector quantities have both a magnitude and a direction.
Give examples of scalar quantities
Speed, distance, mass, time etc.
Give examples of vector quantities
Velocity, displacement, force, acceleration
What is the formula for speed
speed (m/s) = distance travelled (m ÷ time (s)
What is the formula for velocity?
velocity (m/s) = displacement ÷ time
What is acceleration?
The rate of change in velocity
What is negative acceleration often called?
deacceleration
What is the acceleration formula?
Acceleration (m/s²) = Change in velocity (m/s) ÷ time (s)
a=∆v÷t
What is the acceleration formula when time is not given?
(final velocity)² - (initial velocity)² = 2 x acceleration x displacement
v²-u²=2as
What does uniform acceleration mean?
When the acceleration is constant
How can you investigate the motion of a trolley on a ramp?
Set up a ramp with a trolley and have 3 light gates at equal distance from each other. The light gate will record the time when the trolley passes through it. The time taken between the gates can find the average speed on the ramp. Then use the formula of acceleration. This will show the acceleration on the ramp and final speed on the runway
In a distance-time graph what does each thing represent? flat line straight line gradient curve
flat line = stationary
straight line with gradient =Constant Speed
gradient = speed
curve = accelerating or decelerating
In velocity-time graphs what does each thing represent? flat line Uphill line Downhill line area under Curve Gradient
flat line = steady velocity Uphill line = acceleration Downhill line = acceleration area under = displacement Curve = changing acceleration Gradient = acceleration
To find velocity at certain point in the curve on the graph, what do we need to do?
Draw a tangent at that point, and use it to find the gradient of the line
What is a force?
A force is a push or pull that acts upon an object as a result of that object’s interactions with its surroundings.
What is force measured in?
Force is measured in Newtons (N), and has both a magnitude and a direction. Therefore, force is a vector quantity.
What is a contact force?
A contact force can only be exerted when objects are physically touching
What is a non-contact force?
A non-contact force can be exerted without objects physically touching
Give examples of contact forces.
Friction - object and surface touch
Air resistance - object has to be in contact with air
Tension
Normal contact force
Give examples of non- contact forces
Gravitational
Magnetic
Electrostatic
What is a free body diagram?
- Free body diagrams use arrows to show all of the forces acting on an object.
- The length of each arrow indicates the magnitude of that force.
- The direction of each arrow indicates the direction of the force.
What is resultant force?
The resultant force is the overall force acting on an object, taking into account all the different forces acting on it.
What does equilibrium mean?
All the forces acting on the object are balanced.
How do you use scale drawings to find the resultant force?
Draw the forces acting on the object to scale and ‘tip-to-tail’, then measure the length of the resultant force on the diagram. This is the line drawn from the start of the first force to the end of the last force
How do you resolve vectors?
- When you resolve a force, you split the forces into two forces perpendicular to each other. These have the same overall effect as the original one.
- You can use a scale diagram, so just draw two lines so that the original force becomes the longest side of a right-angled triangle
PRACTICE SCALE DRAWINGS AND RESOLVING VECTORS NOW!
I know you haven’t done it and you are going to skip this card, aren’t you? Silly person! This is for your education. NOW DO THEM!
What is Newton’s first law?
- If the stationary object has 0 resultant force, it remains stationary
- If there is a resultant force on a stationary object, it starts moving.
- If a moving object has 0 resultant force on it, it continues moving at a steady speed in the same direction
- if a moving object has a resultant force then it accelerates in the direction of the resultant force.
How does acceleration take five different forms?
- When an object is stationary, it starts moving.
- When an object moves in the same direction as the force, it speeds up.
- When an object is travelling in the opposite direction of the force, it would slow down
- When it travels slowly then it becomes stationary
- The acceleration is because of change in direction without any change in speed
How can you resolve vector? (Give me step by step solutions)
- Measure the resultant force with a ruler and create a scale
- Draw the vertical and horizontal force
- Measure the horizontal and vertical force in cm
- Scale up as necessary to work out the newtons
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 mass of the object
What is Newton’s equation for the second law?
Force (N) = Mass (kg) x acceleration (m/s²)
What is inertial mass?
How difficult it is to change an object’s velocity
What is inertia?
The tendency for the motion of an object to remain unchanged.
What is terminal velocity?
When the object is travelling at a constant velocity due to the forces being equilubrium
Explain the forces on a sky diver.
- As he jumps out of the plane he falls due to weight and there is not much. acceleration
- Acceleration increases as he gets further down but there is air resistance, which is due to the surface area where particles hit.
- It reaches terminal velocity as acceleration is equal to air resistance
- Once the skydiver opens his parachute, there is more surface area so it slows down coming to a stop
What is Newton’s third law?
When two objects interact, the forces they exert on each other are equal and opposite
When pushing against a wall, the wall pushes back with an equal and opposite force. What is the force called?
The normal contact force
What is the formula of momentum?
Momentum (kg m/s) = mass (kg) x velocity (m/s)
What does the conservation of momentum principle state?
The total momentum before a collision is equal to the total momentum after the collision.
What is the force equation including momentum?
Force (N) = change in momentum (kg m/s) ÷ time (s)
Name the different energy stores
Thermal Gravitational potential Elastic potential Magnetic Chemical Electrostatic Nuclear Kinetic
What is the law of energy?
Energy cannot be created or destroyed
List the different ways that energy can be transferred
Mechanically Electrically Through heating Via infrared radiation Via light or sound waves
What is an open system?
Can gain or lose energy to the ‘outside world’
Which two factors determine the strength of the gravitational force of attraction?
The mass of the objects and the distance between the objects
What is the formula for weight?
gravity force (N) = mass (kg) x gravitational field strength (N/kg) W= mg
What is weight?
An object’s weight refers to the force acting on that object due to gravity. This means that an object’s weight can change depending on the strength of gravity. Weight is measured in newtons (N)
What is the formula for gravitational potential energy?
Potential energy (J) = mass (kg) x height (m) x gravitational field strength (N/kg)
What is the formula for kinetic energy?
Kinetic energy (J) = 0.5 x mass (kg) x (speed)² (m/s²) Ke = 1÷2 x m x v²
What is power?
Power is the rate at which energy is transferred, or the rate at which work is done.
What is work done?
The energy transfer that occurs when a force is used to move an object by a certain distance
What is work done formula?
Work done (j) = force (N) x distance (m) W = F x D
What are the two formulas for power?
Power (W) = work done (J) ÷ time (s)
Power (W) = energy transferred (j) ÷. time (s)
What is elastic deformation?
If an object does return to its original shape after the forces have been removed, it is known as elastic deformation.
What is inelastic deformation?
if an object does not return to its original shape after the forces have been removed, it is known as inelastic deformation or plastic deformation.
Applying forces to an object can cause an object to?
- Bend
- Compress
- Stretch
What is extension?
Extension is the increase in length of a spring when its stretched. It can also refer to a decrease in length, if the spring is compressed.
What is the minimum number of forces required to stretch, compress, or bend an object?
Two
What is spring constant?
An object’s spring constant is a measure of how many Newtons of force it would require to stretch (or compress) the object by 1 metre. It has the units N/m. You can think of it as a measure of how stiff the object is. Objects with a higher spring constant are more stiff, so they require more force to stretch.
What is Hooke’s law?
The extension of an object is directly proportional to the force applied.
What is the force applied formula?
Force (N) = spring constant (N/m) x extension (m)
F = EK
What is Hooke’s law practical?
- Have a clamp stand, and a clamp.
- Put the ruler on the clamp stand
- Attach a spring to the clamp
- Put masses on the hook and measure the extension with the ruler
What is the equation for energy transferred in stretching?
energy transferred in stretching (J) = 0.5 x spring constant (N/m) x (extension)² (m²)
What is a moment?
A moment is the rotational or turning effect of a force.
What is the equation for moment of a force?
Moment of a force (Nm) = force (N) x distance (m)
M = FD
D is the perpendicular distance between the force and the pivot
What is the principle of moment?
Total anticlockwise moments = Total clockwise moments
What are levers?
They reduce the force needed to get the same moment.
Where is the net force on the surfaces and what is the formula for pressure?
They are at right angles to all surfaces
Pressure = Force÷ Area
What are hydraulic systems used for?
They use a small force to produce a bigger force.
