Year 7 Physics — Understanding Flashcards

What is a force, in your own words?

A push or pull that can change an object's movement or shape.

What are two main things a force can change about an object?

Its motion or its shape.

Can an object experience a force without moving? Explain.

Yes. Forces can act on an object without making it move. For example, gravity pulls down on a book sitting on a table, but the book stays still because another force balances it.

How can you tell that a force is acting on an object?

Look for a change in motion or shape — such as speeding up, slowing down, changing direction or bending.

What is the difference between a contact and a non-contact force?

A contact force requires objects to touch. A non-contact force can act without objects touching.

Why is pushing a box a contact force?

Because your hand has to touch the box to push it.

Why is gravity a non-contact force?

Because Earth can pull an object towards it without physically touching it.

A magnet attracts a paperclip without touching it. What type of force is this? Why?

Non-contact, because the magnet can exert a force without touching the paperclip.

Why is friction a contact force?

Because friction occurs when surfaces are touching and moving or trying to move against each other.

How could you work out whether an unfamiliar force is contact or non-contact?

Ask: “Do the objects need to touch for the force to act?” If yes → contact. If no → non-contact.

In a force interaction, what is the agent?

The object causing the force.

In a force interaction, what is the receiver?

The object receiving the force.

If you kick a football, how would you identify the agent and receiver?

Your foot is the agent because it causes the force. The football is the receiver because it receives the force.

Can the same object be an agent in one situation and a receiver in another?

Yes. It depends on whether the object is causing or receiving the force.

What happens when two forces act in the same direction? Why?

They combine, making a larger overall force because they are both pushing or pulling the same way.

What happens when two forces act in opposite directions?

They work against each other, so the smaller force is subtracted from the larger force.

If two people push an object in opposite directions, what determines which direction the object will move?

The direction of the larger force.

What does "net force" mean?

The overall force on an object after all the forces acting on it have been combined.

Why is it useful to calculate the net force?

It tells us whether the object's motion is likely to change and in which direction.

What makes two forces balanced?

They are equal in size and opposite in direction.

What is the net force when forces are balanced?

0 N

If the net force on an object is zero, does that automatically mean the object isn't moving?

No. It could be stationary, or it could be moving at a constant speed in a straight line.

What makes forces unbalanced?

The forces don't cancel each other out, so there is a net force.

What can an unbalanced force do to an object's motion?

It can make the object speed up, slow down or change direction.

A football is sitting still. What would need to happen for it to start moving?

There must be an unbalanced force acting on it.

A car is moving at a constant speed in a straight line. What can you say about the forces acting on it?

The forces are balanced, so the net force is zero.

What three things are connected by the formula F = ma?

Force, mass and acceleration.

If you apply more force to the same object, what happens to its acceleration?

Its acceleration increases.

Why is it harder to accelerate a heavy object than a light object using the same force?

A larger mass requires more force to produce the same acceleration.

If two objects experience the same force but one has a larger mass, which accelerates more?

The object with the smaller mass.

What does acceleration mean?

A change in velocity — such as speeding up, slowing down or changing direction.

What is the unit used to measure force?

Newtons (N).

Why do objects fall towards the ground when you drop them?

Earth's gravity pulls them towards the centre of Earth.

Is gravity a contact or non-contact force? Explain why.

Non-contact, because gravity can act without objects touching.

Does gravity only affect objects that are touching the ground?

No. Gravity acts on objects on or near Earth, including objects in the air.

What determines how strongly a planet's gravity pulls objects?

The mass of the planet.

Why is your weight different on different planets?

Different planets have different gravitational strengths.

What is the difference between mass and weight?

Mass is the amount of matter in an object. Weight is the force of gravity acting on that mass.

Which one stays the same when you travel to another planet: mass or weight?

Mass stays the same.

Why can your weight change while your mass stays the same?

Your mass stays the same, but the strength of gravity can change.

Which unit measures mass?

Kilograms (kg).

Which unit measures weight?

Newtons (N).

If gravity on a planet became stronger, what would happen to your weight?

Your weight would increase.

If gravity became weaker, what would happen to your weight?

Your weight would decrease.

What does friction do to moving objects?

It opposes their motion, making it harder for them to move.

Why is friction considered a contact force?

Because the surfaces causing friction must touch each other.

Why can friction sometimes be helpful?

It gives us grip. Without friction, we couldn't walk, hold objects easily or stop vehicles.

Why can friction sometimes be a problem?

It can slow objects down and cause energy to be transferred as heat

What would happen if there were almost no friction between your shoes and the ground?

You would have very little grip and would probably slip.

Why is running on ice difficult?

Ice provides very little friction, so your shoes have less grip.

If you reduce friction acting against a moving object, what will generally happen to its motion?

It can move more easily and maintain its speed more easily.

Why does oil make surfaces easier to slide across?

Oil reduces friction between the surfaces.

Why would an object generally move more easily across oiled metal than sand?

Oiled metal provides much less friction, while sand creates more resistance.

Why don't we always want to reduce friction as much as possible?

Because some friction is useful for grip and control.

Why do swimmers want to reduce friction and drag?

So they experience less resistance from the water and can move more efficiently.

Why might a swimmer wear a specially designed swimsuit rather than a loose T-shirt?

A specially designed swimsuit can create less resistance through the water.

Give one situation where you WANT more friction and one where you WANT less friction.

More: shoes gripping the ground.
Less: skis sliding over snow.

A book is sitting still on a table. Gravity is pulling it down. Why doesn't it fall through the table?

The table provides an upward support force that balances the downward force of gravity.

A cyclist stops pedalling but eventually slows down. What forces could explain this?

Friction and air resistance act against the cyclist's motion.

A toy car moves faster when you push it harder. What does this tell you about force and acceleration?

A greater force produces greater acceleration when the mass stays the same.

Two identical shopping carts are pushed. One is pushed with twice as much force. Which accelerates more, and why?

The cart with more force accelerates more because acceleration increases when force increases.

An astronaut travels to the Moon. What changes and what stays the same: their mass, weight and gravitational force?

Mass stays the same. Weight and gravitational force decrease because the Moon has weaker gravity.

A car is travelling forwards, but the forces acting on it are balanced. Is it necessarily stopped? Explain.

No. Balanced forces mean its motion isn't changing. It can continue moving at a constant speed in a straight line.

A ball is moving to the right but experiences a force to the left. What might happen to the ball?

It could slow down. If the force continues and is strong enough, it could eventually stop and then move left.

You want a box to slide more easily across the floor. What could you do to reduce friction?

You could make the surfaces smoother or use a lubricant such as oil.

Why would making a surface rougher sometimes make an object harder to move?

A rougher surface can create more friction, which opposes the object's motion.