Physics Topic 5 Flashcards
A force is a push or ____ that acts upon an object as a result of that _________ interactions with its surroundings.
pull
object’s
Force is measured in _______ (_), and has both a m________ and a d_________.
Therefore, force is a v_____ quantity.
Force is measured in Newtons (N), and has both a magnitude and a direction.
Therefore, force is a vector quantity.
A ________ force can only be exerted when objects are physically touching
A ___-_______ force can be exerted without objects physically touching
contact
non-contact
Give 2 examples of a contact force:
Normal contact force
Tension force
Friction force
Give 2 examples of a non-contact force:
Electrostatic force
Gravitational force
Magnetic force
Is air resistance a contact or non-contact force? Explain why.
Air resistance is a contact force. This is because it is due to the physical contact (collisions) between an object and the particles in the air.
______ quantities only have a magnitude and do not have a direction.
______ quantities have both a magnitude and a direction.
Scalar quantities only have a magnitude and do not have a direction.
Vector quantities have both a magnitude and a direction.
Give 2 examples of scalar quantities.
Temperature
Distance
Speed
Give 2 examples of vector quantities.
Weight
Displacement
Velocity
Shown is an image of a moving car with a 25km arrow pointing in the EAST direction.
In the diagram above, what does the labelled arrow represent?
Displacement, which is a vector quantity
A 20 m displacement North is the same as:
-20 m displacement South
A women walks 500 m from her home to the shop. She then walks 200 m to the park and finally 400 m back to her home. What is the overall distance and displacement of her journey?
Distance = ____ m
Displacement = _ m
Her total distance is the 500 m + 200 m + 400 m so 1100 m in total.
However, as she returns to her house, her displacement is 0 m, because she ends 0 m from where she started.
A man cycles 12 km south east.
-> What does the 12 km represent?
-> What does the south-east represent?
Magnitude
Direction
Is power a vector or a scalar quantity? Explain your answer.
Power is a scalar quantity, because it only has a magnitude (how many watts), it doesn’t have a direction.
<–
What does the way the arrow is pointing represent?
What does the length of the arrow represent?
Direction
Magnitude
Free body diagrams use arrows to show all of the __________ acting on an object.
The length of each arrow indicates the ___________ of that force.
The direction of each arrow indicates the ___________ of the force.
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 the resultant force?
The resultant force is the overall force acting on an object, taking into account all the different forces acting on it.
Forces acting in opposite directions on the same object can ‘cancel out’.
During take-off, a plane has a lift force (upwards force) of 690,000 N and a weight (downwards force) of 600,000 N.
What is the resultant force acting on the plane?
90,000 N upwards
Resultant force?
20 N –> O <– 10 N
10 N to the right
Resultant force?
5 N –> O <– 30 N
25 N to the left
Resultant force?
|<– 45 N
60 N –> | <– 15 N
0 N - no resultant force
If all the forces acting on an object balance out, then we say that the object is in:
Equilibrium
The stick with wheels above is travelling at a constant velocity because the forces acting on it are in equilibrium.
What is the missing force?
|–> 900 N
1700 N <– |–> ? N
Therefore, the missing force must have a magnitude of 800 newtons to the right.
The term ‘deformation’ refers to…
… a change in the shape of an object as a result of forces being applied to it.
If an object does return to its original shape after the forces have been removed, it is known as __________ deformation.
On the other hand, if an object does not return to its original shape after the forces have been removed, it is known as __________ deformation (or sometimes plastic deformation).
elastic
inelastic
Applying forces to an object can cause it to (Give 3):
Compress
Stretch
Bend
________ is the increase in length of a spring when its stretched.
Be aware that it can also refer to a decrease in length, if the spring is compressed.
Extension
What is the minimum number of forces required to stretch, compress, or bend an object?
Two.
Remember: if only one force is applied to an object, it will just move, and it won’t stretch, compress, or bend.
An object’s ___________ 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 _______ force to stretch.
spring constant
more
Which object do you think has the higher spring constant?
A bungee cord
A plank of wood
A plank of wood
What does a higher spring constant mean?
More energy is required to stretch it or, in other words, is more stiff (less elastic).
What does Hooke’s Law state?
Hooke’s Law states that the extension of an object is directly proportional to the force applied.
If you stretch an object too much it can pass its ‘elastic limit’ (also known as the ‘limit of proportionality’).
At this point what will happen to the object?
It will start deforming inelastically
Hooke’s Law is the formula:
F=ke
Every spring has a characteristic called the spring constant, which is a measure of how firm the spring is.
A ______ spring constant means the spring is more firm.
A _____ spring constant means the spring is less firm.
higher
lower
The formula that links force and extension is:
F = ke
A spring has a spring constant of 120 N/m, and an unstretched length of 0.5m.
What force is required to stretch the spring from 0.5m, to 0.6m?
F = ?
k = 120 N/m
e = 0.6 - 0.5 = 0.1 m
F = 120 x 0.1 = 12N
A force of 5 N is applied to a spring, causing it to stretch from a length of 0.1 m, to a length of 0.15 m.
What is the spring constant of the spring?
F = 5 N
k = ?
e = 0.15 - 0.1 = 0.05 m
5 / 0.05
= 100 N/m
When a spring is stretched, energy is transferred to its _______ potential energy store.
Then when the spring is released, most of that energy is transferred to _______ energy.
elastic
kinetic
The formula for elastic potential energy is:
Ee = 0.5ke2
A spring with a spring constant of 4 N/m is stretched by 0.5 m.
How much elastic potential energy did it gain?
0.5 x 4 x 0.5 squared
0.5J
A scalar quantity only has magnitude.
A vector quantity has both magnitude and ________.
direction
A person is walking 1.5 m/s north.
This is an example of:
velocity
Distance is a ______ quantity whereas displacement is a ______ quantity.
scalar
vector
A dog travels 300 m north in 100 s.
What is the dog’s average velocity in m/s?
3 m/s
Acceleration is:
The rate of change in velocity
Negative acceleration is often called:
deceleration
On a velocity / time graph, the distance travelled is shown by:
The area under the curve
A flat line on the velocity / time graph tells us the object is moving at constant ________.
velocity
On a velocity / time graph, the velocity is on the _-axis, and the time is on the _-axis.
y
x
On a distance / time graph, the distance is on the _-axis and the time is on the _-axis.
y
x
The force that causes an object to fall towards the earth is:
Weight
The size of the air resistance is dependent on the object’s ______.
surface area and velocity
True or false? The force of air resistance is caused by the moving object colliding with particles in the air.
True
As the velocity of a falling object increases, the air resistance:
Increases
We say an object has reached ‘terminal velocity’ when it is falling with a _________ velocity.
constant
Terminal velocity is reached when: give 2
The resultant force is zero
The weight has the same magnitude as the air resistance
If a ball is dropped from a plane and has not yet reached terminal velocity, then the ball must be:
The balls weight must still be larger than its air resistance, and so it will be accelerating.
Newton’s first law?
A resultant force is required to change the motion of an object.
A moving object that has no resultant force acting upon it will:
Continue moving at the same velocity
Newton’s second law?
A resultant force will cause an object to accelerate in the direction of the force.
Which of the following could not be caused by a resultant force acting on an object?
The object slows down
The object speeds up
The object changes direction
The object maintains constant velocity
The object maintains constant velocity
What is an example of circular motion?
The moon orbiting the earth.
An example of circular motion is the moon orbiting the earth.
Give 2 points which are true:
The moon is moving at a constant speed.
The moon is accelerating
The formula for Newton’s second law is:
F=ma
A object has a mass of 4 kg and is accelerating at 3 m/s2.
Calculate the resultant force acting on the object.
F=ma
4x3=12N
A resultant force of 30 N acts on a 12 kg object.
What is the object’s acceleration?
F=ma
30/12 = 2.5 m/s2
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.
This force is called:
The normal contact force
Anna hits a nail with a hammer. During the collision, a force is exerted:
On both the hammer and the nail
A person weighs 800 N and is standing on the ground.
The ground is pushing upwards towards the person’s feet. How many newtons is this force?
800N
Newtons third law says that when two objects interact, the forces they exert on each other are equal and opposite. So if the person exerts 800 N on the ground (his weight), then the ground must also exert 800 N up on him (normal contact force).
What is the total distance called when a car travels from the moment when the driver first notices an obstruction, to when the car stops?
‘Stopping distance’
Stopping distance equals:
Thinking distance + braking distance
Give 3 factors which would slow a person’s reaction time:
Consuming alcohol
Being distracted
Tiredness
Give 3 factors which would increase the braking distance:
Worn tyre tread
Worn brakes
Ice on the road
A vehicle drives twice as fast.
What happens to the breaking distance?
The breaking distance increases by four times
If the vehicle speed increases by a factor of 2, then the breaking distance will increase by a factor 2 squared (22), so 4 fold.
Give a factor which affects both the thinking distance and the braking distance:
Speed of the vehicle
The formula for momentum is:
Momentum (p) = mass (m) x velocity
Momentum is a __________ quantity.
Momentum has both magnitude and direction, so is a vector.
The units for momentum are:
kg m/s
The conservation of momentum principle states:
The total momentum before a collision is equal to the total momentum after the collision.
The total momentum before a collision is 300 kg m/s.
What is the total momentum after the collision?
300 kg m/s
