Forces that need touch

The idea

Forces that act only when there is physical contact between objects, direct or indirect (through a stick or rope), are called contact forces.

Touch or not

You open a drawer by pulling its handle. You pull a cart with a rope. You push a box with a stick.

In these cases, is there contact between objects?

• Yes, direct or indirect
• No contact at all
• Only in one of them

Needs contact?

Tap the bin where each force belongs.

Touch, direct or indirect

In some forces, a body part touches the object directly. In others, a stick or a rope is between you and the object. Both need contact.

Forces that act only when there is physical contact between the objects are called contact forces. The contact can be direct (hands or body parts) or indirect (a stick or a rope).

• Example | Contact
• Hand on a table | Direct
• Stick on a box | Indirect
• Rope on a cart | Indirect

Notes

Forces that act only when objects touch are contact forces. The contact can be direct or indirect, through a stick or rope.

Check yourself

Forces that act only when objects touch are called …

Pushing a box with a stick is a case of …

Pulling a cart with a rope needs …

Which of these is a contact force?

• non-contact forces. Non-contact forces work even without touching.
• balanced forces. Balanced forces are a different idea. Touching forces are contact forces.
• contact forces — correct. Yes!
• indirect contact — correct. Yes!
• direct contact. Your hand touches the stick, not the box. The contact is indirect.
• no contact. The stick touches the box, so there is contact.
• no contact at all. The rope touches the cart. Contact is needed.
• contact through the rope — correct. Yes!
• contact only with the ground. The force on the cart comes through the rope.
• A ball falling to the ground. The Earth pulls it without touching it. That is not a contact force.
• A magnet pulling a clip from far away. It works without contact.
• Pushing a table with your hand — correct. Yes!